<Snipped quote by Burthstone>
Huh, I actually found that there were a bit more random one-shot attacks in Bloodborne. But you never really noticed it because you're so mobile in Bloodborne compared to Dark Souls, so you don't get hit by them very often. Unless you're me, and you need to git gud.
Odd, but I think it's a vitality stat problem then, I only get one-shot when I'm under leveled in a Chalice Dungeon (Beat one boss that I used all my ammo on, most got visceral attacks off, and I barely won, but that boss had easy to predict attacks) or let a really really obvious death attack from a boss hit.
Then again I'm mostly through NG+ now and I have yet to be truly frustrated with a (non-chalice) boss, and I'm also in NG+ in Darksouls uno (Haven't done anything there though), so maybe I'm just half decent at the game.
BTW you can get out of grabs by spamming the bumper and trigger buttons.