1 hits have always been the most irritating thing. Not for the fact of whether or not they are telegraphed, but they are 99% impossible to gear check, except in rare cases with barbarians. It would be nice to eventually grow enough in power to survive these abilities, be it with charms only or other methods. Have it be like a case similar to the arrowsider proc in TA is a start, thought granted the desyncing arrows are.... left to be desired

Qouv Tsin is quite overlooked. Literally the hardest part about this boss is clearing Stony Tomb if you first enter destruction. He gives quite a powerful charm, for a boss that can literally never kill you once you have stacked enough resistances. He could use quite the repainting.
Bull Prince Rodeo is fun fighting outside of the wall cheese, but it would be nice seeing him get a replaced ability for stampede to change the pace of the fight. Having the walls completely negate one of his abilities means that he doesn't have an ability at that point.
Triune farming for cycle is a nice ulta endgame place to farm, Sewers is a nice place to farm early and I love em both for that. Triune's boss though is left to be desired. Having to control finicky AI, being obnoxiously teleported around when I had perfect placement. And to top it all off, completely forgetting I had to re-equip the charm every death made me waste so much time. Half my own stupidity, half salt.
Laz is very fun to fight, and has quite the skillcap on it to boot in order to do it deathless (note: have not done so yet). The avoid tacked onto him is no so much. Laz is a positional punishing fight, one mis-step and your dead. Suddenly missing a purify because of a diceroll immediately kills the fight's enjoyment. Just having more HP would of done it really.
Thats all I can think about right now. Theres probably more but candy calls me...