Why Combo when Bosses don't give you enough time......

The whole issue with skills in this game is the amount, One skill doesn't do all you need, they are designed in a way where they need another similar skill to synergize with, especially leveling through campaign its very evident, the pacing everything although slow feels good and well thought out.

However...

Endgame is a trainwreck, I try to build up combos between 3 abilities, grenades, 2 different ammo, 1 mark, followed by 2 banners

Learned that by the time I electrocute the enemy I only have enough time to armour break with piercing rounds and spam high velocity

If I don't already have a banner down, and I try placing banner first, by the time I armour break he's no longer electrocuted, and I lose out on DPS for him not being immobilized.

+ I Always need to have my mark active on him and that interferes as well, no support gems to increase mark speed? only passives? its just not fun in endgame with all these skills and MILISECONDS TO REACT, either more time inbetween boss phases, or just more hp to boss, and scale back damage so we aren't only dying to one hits, its just not fun, and the reward? very lacking

Yeah, I mostly agree. The boss mechanics feel like they go from 0 to "blink and you're dead" way too early. For a newer player it's not "learning a fight", it's "learning a respawn screen". Fast is fine, but fast with no runway just punishes you without teaching you anything.

PoE2 really needs some kind of built-in pacing curve for bosses. Early attempts should be slower so you can actually read what's happening. Then, if the fight drags on, ramp the mechanics up a bit each "round" so you can't just noodle the boss forever. Not infinitely faster, just enough to say "okay, time to execute" without turning it into a twitch audition.

Also, bosses should have tiers or levels. A beginner tier shouldn't be handing out instant death like party favors. An expert tier absolutely should. If you're signing up for the "I know this boss in my sleep" version, then yeah, you get punished accordingly. That's the whole flex, can you handle the highest tier and still win.

PS: I play minions, and honestly it feels a little silly sometimes. I can run laps to dodge one-shots while my zoo keeps chewing on the boss. They die occasionally, sure, but then they pop back up in seconds and we're back to business. Feels kinda OP... but also, that's literally the point of the build, so I'm not exactly filing a complaint.

Likely intentional so you cant stack too many multiplers on combos.