Difficulty off bosses depends a lot on your build and your dexterity, largely your ability to not get hung up on level geometry and either get swarmed or slapped in the face repeatedly by the big baddie. Often running forward and around the boss is better than the instinctual backpedaling.
I’m at WT 10 and feel no real need to push it any more. Most stuff drops like flies to Blight/Toxic anyhow, and it’s only a few types of bosses that are annoying. I’m 26 or so I think, and have done all the assassination quests and nearly all of the critter quests, and I still have a bit to go to the so-called end game.
Blight/Toxic + large capacity weapon + the right mods + Perpetuum Mobile = mass death machine.