Biggest problems:
Some core specs are completely not viable in in casual fun. Core engi, core warrior, and to some extent core mesmer. Firebrand is rather weak now, too.
Some specific traits are overpowered on their own, regardless of how good or bad a build is; Ie, Juggernaut trait in Firearms line for Engineer giving infinite stability to a flamethrower wielder.
Some utility and weapon skills are too strong on their own for their cool down periods - Icerazor's Ire and Darkrazor's Daring are only on 12 sec cooldowns which is more like 10 second cooldowns once you consider Orders from Above's alacrity bonus.
Some utility options are genuinely too weak to be viable in the vast majority of contexts: for example, Bomb Kit's 240 radius AOEs are too weak for the amount of damage a user should expect via either conditions or direct damage, and the pulsing or single-instance period of the conditions or effects is too low to justify for utility purposes, at least in PvP. Same for elite skills - some skills like "Chilled to the Bone" are now so weak compared to skills like Liche Form in terms of EVERYTHING that there are no remaining applications for the skills; you will always do those weak skill's effects AND then some choosing something else.
This goes for a lot of CCs at large - there's inconsistency with the "No Dmg for CC" rule in that Swipe and Fear and Lightning Rod can do damage while CC-ing (and then there's Explosive Entrance that activates on hit), but a lot of weapon, utility, and elite skills do no damage anymore really hurting their use cases.
There are also a lot of tanky builds - despite removing Barbarian, Knight's, and Cavalier's amulets from the game and weakening Paladin's amulet, there are builds that are able to bunk nodes 2v1 in most scenarios, save for +1 by a thief. Bunker durids, condi heralds, condi renegades, condi rangers, burn guards and DHs, hammerbreakers, core necros, decap scrappers, fire weavers, and staff daredevils can all just sit on a node and bunk all game and it's not worth it to move them in most cases without a coordinated effort, sort of impossible to do in ranked. Maybe in ATs, but not in ranked. They might technically be "balanced" on paper but they take away so much fun out of a game because how much they slow it down.
Then there are builds that are arguably fairly counter able but hard counter some other classes way too strongly, especially in the hands of a good player, to be warranted. Namely condi thieves and dragonhunters running Rune of the Trapper, and also holosmith running grenade kit. They might be "balanced" but it's not fun to fight them in any context. Balance should be built on your ability to outplay your opponent in a 10-15 second time window 1v1 rather than on who snipes their burst first and forces the other player to submit to conditions and control effects.
Lastly, some builds have access to condition spikes that defeat this supposed philosophy of "damage over time" for conditions - burn guards, condi thieves, condi rangers, scourges, burn weavers, condi revs, and to some extent condi mesmers as well. If it is damage over time, it shouldn't spike 15K damage in 3 seconds.
Also, the longevity of some conditions at a base are way too long - Ranger traps that put multiple stacks of poison on you for 12+ seconds and Renegade's Sevenshot with it's base torment duration of 7 seconds are just too long. furthermore, No application of immobilization should last longer than 2 seconds, that's too much for decent counterplay.
Lol Renegades just switched to Shiro and are still the driving force of games by CC, dmg, and conditions AND are tanky AND fast AND port.
