I agree with you really. My initial reaction to the boss was "Cleric Beast 2.0, really FromSoft? Jeez..." But then I died to it like 40 times or some shit and yeah, it does have some unique attacks and phases so it sort of redeems it but still leaves a bad taste in my mouth after experiencing the other bosses, most of which are godtier.
Which boss are you asking about? For reference, I had 40 Vit the whole time, and I'm sitting around level 187 or so. I booted up Bloodborne Monday night and realized I was at the beginning of NG+++, so I hauled ass through Cleric Beast, Gascoigne, and Amelia, then went straight to DLC so I'm a bit underleveled for the NG level I think. I'll list some things that one-shotted me with >80% health (Just a bit of variance from having full health cause I wasn't always aware of my health pool when instantly dying lol. I just knew I was very high and wasn't concerned about having to use a vial.)
Ludwig's charge attack
Ludwig jumping and falling on top of me
One of Maria's phase 2/3 power attacks.. Can't remember which, but it happened once to my surprise. (Otherwise her attacks were doing like 40-60% damage per hit, which was already pretty brutal.)
I don't remember any of the Living Failures attacks 1-shotting me.
Orphan's phase 1 leaping slice attack sometimes 1-shotted me from ~80% health or more.
Laurence had a few. His opening atttack, that fist slam on the ground that explodes? That 1-shots if it hits you, even before the explosion. If he jumps and lands on you, that 1-shots you. I'm fairly certain if he grabs you, it does enough to kill you even at full health.
Hope that helps! It's very difficult but sooo rewarding once you defeat them.
Oh and I totally agree with you, I wish there was a boss rush mode or a boss select mode like customizing chalice layer bosses or something. That would be AMAZING. :O