I'm going to cover what I've seen to be true in my experience pugging raids and fractals. The typical roles and comps are usually very different from what snowcrow's or dt's sites label "meta." Usually, the only thing that really carriers over from the Snowcrows benchmarks pages to pugs is whether condi or power DPS is more effective, with the exception of Dhuum where the majority of pugs bring condi damage. I'm not saying that these comps are the best or most effective or that I advocate for them, but am simply saying that this has been the "pug meta" and mindset in my experience.
In raids, most groups nowadays follow this comp template:
1. Chrono for tanking and quickness
2. Druid for might, spirits, healing
3. Heal Firebrand for quickness to second subgroup and second source of healing
4. Banner Berserker ("BS," with condi and power variants depending on boss)
5. Renegade that provides alacrity to 10 players
6. 5 DPS slots
Boss to boss and pug to pug, the composition of may differ (such as dropping a DPS to add a third healer), but this is what I generally see advertisements looking for.
Quickness:
Due to nerfs to signet of inspiration, chronos are no longer the favored class to provide either quickness or alacrity, and are only taken in a support role when they are required to tank. In most cases, there will still be a chrono tank and heal firebrands ("healbrand/hb") are usually the go-to for pugs to cover quickness for the second subgroup, due to the role compression of a healer and support all in one. I know snowcrows lists their "power boon chrono" as "meta" and extremely common in pugs, but I have never seen LFGs or squads looking for one, and chrono tanks still tend to run some mix of toughness in their gear (toughness needs to be greater than 1150 because power soulbeast gains 150 in its build) while using a shield for the blocks and Tides of Time.
When running only one healer or an alternative healer to the healbrand, condi quickness firebrands ("condi quickbrand/cqb") are the default quickness giver that most pugs turn to. Simply, condi quickness firebrands do more damage than your average quickness chrono in diviner's gear while having an easier time maintaining quickness (pressing an easy button for AoE quickness instead of needing to ramp up clones to shatter). Rarely, you might run into chronos that give 10 man quickness due to having full diviners gear and/or 100% boon duration, but in my opinion this build would only be worth it on Conjured Amalgamate, which heavily favors power over condition damage, benefits greatly from the mesmer focus pull to pull in conjured adds, and does not have a traditional tank role that would require a chrono tank. Keep Construct is another boss where non-tank quickness chrono may be better than condi quickness firebrand, but generally here, most pugs bring a tank chrono and healbrand anyway.
On Matthias, Adina, and Mursaat Overseer, a boon daredevil is used instead to provide 10 man quickness due to Steal giving the thief the skill Detonate Plasma, that gives all boons except alacrity to 10 players. While harder to find in pugs, they are still generally common enough that you may sometimes run across them in the LFGs. When pugs don't have a boon thief, they just take the traditional double condi quickness firebrand on these bosses. There is a core thief version of this build but no one really plays it.
Alacrity:
Renegade is the king of this role now. In all non-condition favored fights, the pug meta is to take a single power-based support renegade ("alacrigade") with the trait Righteous Rebel to give 10 man alacrity. Even in fights where power isn't as effective as condition damage, many pugs still rely on only a single power renegade to provide 10 man alacrity, because it is a bigger pain to advertise and seek out more specialized roles.
The alternative to a single power renegade for alacrity is to run 2 condition dps renegades (referred to as "RR") who both take Righteous Rebel but also have 0% boon duration (hence why you have two players take RR instead of just 1). In my personal opinion, pug player skill pressing the alacrity button is so poor that many groups would probably benefit from 3 condi RR renegades instead of 2, but when pugs do ask for condi RR renegade, they only ask for 2. This is more common and oftentimes more optimal on fights where condition damage is needed, which include Matthias, Cairn, Soulless Horror, Dhuum, and Qadim the Peerless. In my opinion, condi RR is also the better choice for Mursaat Overseer (great damage and will help the scourge's epidemic) and respectable on Sabir, but pugs will often just ask for your simple power renegade due to ease of finding one for both these bosses and in general.
Renegade is not used on Twin Largos. This fight is the only one of its nature where not stacking 8 mesmers and 2 druids is almost a mechanical failure in itself. For this fight, alacrity is "provided" by the chrono tank. I put provided in quotes because while in theory the tanks should be running both well of alacrity and some boon duration, alacrity uptime for non-chronos in this fight is horrid in pugs due to no one standing in wells.
Tanking:
The pug meta for all bosses that require a tank is to take a chrono with variable amounts of boon duration and toughness. Everyone seems to build a bit differently so there's no set pattern that I've seen in my experience. Tank healbrands are also accepted by pugs in all instances where a chrono would be, although the actual difficulty of tanking on a healbrand will be different depending on boss. I don't usually tank, so I'm not the most experienced on this topic, but I'd say that healbrands are generally more common when tanking the "easy" bosses and bosses that don't multi-hit (like Qadim the Peerless or Xera), though pugs readily accept them at every boss aside from Largos. Notable exceptions to the "easy" rule where I have seen healbrands tank sometimes are Deimos and Dhuum, due to their attacks being relatively slow and able to be blocked with aegis.
Tanking on Adina is usually done on a heal renegade or (less commonly) the boon daredevil since quickness givers aren't needed outside the daredevil, but that's the only exception you'll see for tanking from the standard chrono/healbrand.
Contrary to the Benchmarks page on Snowcrows, no one uses druid tanks in pugs (maybe you might rarely see one on gorseval if that's the only boss the group does).
Healers:
Druid is taken on every fight in pugs, no exceptions. You're not going to see any fancy groups running soulbeasts for spirits instead, trying to squeeze out extra DPS. Sometimes, pugs may only take one healer. In my anecdotal experience, these groups are almost always your "elitist," one-pull-or-leave-type groups. As mentioned before, healbrand is the default second healer 90% of the time.
Alternate heal options include heal renegade and less commonly heal tempest, although groups rarely explicitly advertise for these roles and when you do see players playing these classes, they either join because the listing posted a vague "looking for offheal" message that didn't force them into healbrand or they don't have a healbrand geared (in these cases the group would have condi quickbrands).
Heal renegade has its pug meta place for fights that need use of the ventari bubble, notably Adina. Bubble renegade (either heal or power dps) may also be used at Sabir to block the wisps.
The "noob" healer that are almost taboo in the pug meta is the heal scourge, due to its reputation of carrying bad groups and bad players kicking and screaming to success (see Boneskinner in strike missions as an example, where pugs have just given up on dodging mechanics). In my opinion, this reputation is undoubtedly true and it is, I think, the best healer in the game by far. Groups will rarely ask for one, but beginner groups won't be shy about running them. Ironically, because of just how heal scourge is just too good at carrying, they are sometimes unwelcome by commanders and pugs, who will try to shame you with the "git gud" attitude and scoff at the notion that they of all people would need a heal scourge to peel their skin off the ground. In my opinion, this mindset is unfortunately misplaced if you're a pug who is only looking for easy, consistent clears, but that's how it is.
DPS:
GW2 has come a long way from the reaper stigma you mentioned. For the most part, all DPS builds that have a page on snowcrows (the ultimate legitimizer)are welcome, except for I have never seen a herald in raids (so you won't be seeing boon heralds in Samarog in pugs). Condi scourge also tends to not DPS well and will often fall behind the banner berserker, and is not turned to as a DPS option unless epidemic is needed. The only requirement here is that you bring the appropriate type of build (condi or power) to the fight. Even then, pugs are really only sometimes sensitive to this for Keep Construct, maybe Slothasor and Conjured Amalgamate.
Pug meta relevant DPS builds include, in order of general efficacy in the hands of your average pug player (in my opinion). These are obviously variable depending on player skill:
Power: Holosmith, Soulbeast, Chrono, Weaver/Tempest, Dragonhunter, Daredevil, Reaper
Condition: Firebrand, Mirage, Renegade, Soulbeast, Scourge
Other high DPS builds exist out there of course, such as condi weaver and DPS berserker variants, but these are rarely seen. I ranked power chrono and dragonhunter fairly low due to the lack of slow and retaliation uptimes that each build respectively requires in pugs. Other than those exceptions, these basically follow your snowcrows benchmarks for the most part.
With all that said, doing top/near top DPS regardless of build or profession will keep everyone's mouth shut.
Exception here is Twin Largos, where at the minimum, you must run a condi build for pugs. Ideally, pugs would have nothing but condi chronos and mirages here simply because a mediocre mesmer player is often just as good or better than a great player of any other build.
In fractals, the pug meta is:
1. Healbrand
2. Power Alacrigade
3. Power Banner Berserker (although some groups may skip on this in favor of a third DPS)
4. 2 DPS slots
Notes for alacrity/quickness are the same as for raids. No one runs chronos in fractals becomes nobody stands in your alacrity wells, and mobs die too fast for chronos to generate the clones that are shattered for quickness, thus the ubiquity of firebrands. On T3 and below fractals (eg. recommended fractals), you may find condi quickbrands replacing healbrands. Sometimes, the group may have a condi quickbrand and instead use a heal renegade as a healer, but this is not very common and healbrands are preferred over heal renegade for the firebrand's greater range of utility, blocks, and heals in general.
My understanding is that druids are not taken in fractals because groups usually aren't stacked as tightly to benefit from the powerful close-range celestial avatar healing, and the DPS loss isn't worth it. Better to bring a healbrand that compresses the roles of quickness and healing than having a dedicated druid healer and a lower DPS condi quickbrand, even after spirit buffs. At least this is what I think the reasoning is.
In terms of welcome DPS classes, power is heavily preferred although no one can really tell what build you are coming in, and once again, pulling high DPS shuts everyone up. The exception to this is for 100cm, where condi is the pug meta. In fact, most 100cm pug groups (especially those that require kill proof) exclusively take 3x condi firebrands, 1 alacrigade, and 1 healbrand, and will take no other composition.
Quick note on the builds that dt marks as "meta." No one runs power firebrand for quickness. You either get the quickness from a healbrand, or you get it from the condi quickbrand. As soon as the encounter lasts >60 sec (approximately if I remember correctly), condi quickbrand out-dpses power quickbrand. You'll encounter weavers, but they are by no means the common "meta" dps choice. Same for soulbeasts, who you cannot rely on to bring frost spirit.
Might isn't super coordinated in my experience, although the residual might that many builds generate is supposedly enough. I suppose the hope is that your healbrand uses staff 4 once in a while, you brought a power banner berserker who is bringing the tactics line for soldiers focus, and that your alacrigade also remembers to use the F2 Heroic Command.
EDIT: I edited my comments about DPS classes. Pugs are more accepting of any random DPS class than I might've implied.
