I don't see this. I found Malenia, Fire Giant, and Maliketh to all be phenomenal. Elden Beast and its precursor fight were solid, but a tier or 2 below the other 3. The duo fight is a duo fight, so fine.

Yeah, a lot of early games "bosses" are late game basic enemies. Which kind of makes sense - you aren't fighting a unique, named enemy: You are fighting a powerful enemy that will eventually be a regular mob (which is something done in other Souls game like the Taurus Demon in the first Dark Souls). Personally, I really didn't notice/feel the repetition until 80/90 hours in of my 130-140 hour play through. And at that point I was transitioning to the end game that felt newer and lessened the feel of repetition.