I don't know if Bloodborne is "easier" than the rest of the souls series so much as it's a lot friendlier towards being aggressive and actually puts every boss fight at your level, where even giant dudes suffer through the same mechanics you do. I was surprised at how much more intuitive stunning enemies with guns was than trying to parry their attacks with shields. A lot of the later boss fights in Dark Souls 1/2 are just outright cheap rather than difficult too. It's a little hard to compare.
Also funny that you say the One Reborn was hard, cause he as a chump for me. Ebrietas, Paarl and some of the Chalice dungeon bosses would constantly wreck me though, specially the later. Do those if you haven't already, I'm pretty sure their difficulty is "fixed" outside of NG+ rules.