not sure if my dick is just fucking HUGE, but i haven't encountered any bosses so far that are a serious problem for me. I've beaten Balteus and Sea-Spider. Sea-Spider was under 5 tries, Balteus was probably closer to 20, he is by far the hardest so far, but still completely manageable. you just have to be hyper-aggressive and beat his ass.
my current build is gatling gun and assault rifle, i use the gatling for extreme pressure to break posture, when the gatling has to cool down, i use the assault riffle to make sure the posture bar doesn't decrease. once posture is broken, i swap out the assault rifle for pilebunker and absolutely shit on people. pilebunker does like 55% HP to some guys in the arena and like 15-20% to bosses. just completely fucks their day up.
honestly confused on the people who bought this game and are just getting dumpstered because like, Margit in Elden Ring was a way bigger wall for me than anything in ACVI so far.
edit: oh i forgot to mention, the game has an audio que, two beeps, which usually means an enemy is locked on and about to rape you with something. if you just dodge where the third beep would've been in the que, things get a lot easier. Balteus for example fires like a grenade or missile at you that hurts real bad if you don't listen for that que.