I brought this up in one of the other Nioh threads a couple weeks ago. I also felt that the boss fights, at least in the last trial, were a little bit too unforgiving. I didn't have as much trouble killing the Watchdog in Bloodbornes Chalice Dungeons as trying to beat the ogress boss. Imo they do too much damage, have a too large health pool and the hitboxes felt worse than in some of the Dark Souls negative examples.
I can't say I had nearly as much trouble with her, it was about on par with Bloodborne for me. I can see where the criticism regarding the health pools comes from, especially if you want to stay agile and focus on low stance, but the hitbox thing I can't agree on. Once I figured out the bosses' movesets precisely, I never had any issues with unfairly getting clipped by their attacks.
After beating her once, I started throwing my whole arsenal at her to see how that all works/feels/whatever, and it was definitely the most fun I had with her. I'm talking about your rechargeable spells, buffs, guardian special attacks and so on. Using all those tools in conjunction with regular melee made the fight surprisingly fast.