I like the idea of TF2-like tradeoffs instead of upgrades. I think that analysis by OP is superficial but nonetheless. I won't be able to digest the whole thread but I think I would chip in my 50c here regarding engi, mostly for PvE.
**Holo** is OP. It especially feels OP compared to the core which has no powerful third traitline to offer. This is well known.
The biggest _gain_ of holo is dps scaling based on heat. It is so powerful it overshines everything else. Even condi these days are holo which makes no sense for a "spiky" spec.
The biggest _drawback_ is not even F5 toolbelt skill which is always pretty situational and mostly for PvP honestly. It's that you cannot get out of the forge for 6 seconds. This might not seem like a big deal but please remember: engi is a profession with constant kit swapping with virtually no cd. So you are sacrificing your kit piano-like playing for forge. Yes, you need pay attention to the heat and so on so you need strong sense of when to heat up but it's a skill ceiling and can be learned, it's not something that's balanced when you learn it.
Like many people I really like the _idea_ or _flavor_ of core engi but it's so weak that it has no place anywhere across the game.