Manus was designed as they started designing Bloodborne so yeah they kinda reused some ideas there. I think Manus is harder than most Beast Bosses though. Fuck you Laurence.
So far Manus hasn't been as hard as Artorias, but making mistakes with him is even more punishing than with Artorias because he does that fucking combo where he just pummels you a bunch, also the fucking magic.
The souls games cannabalise each other constantly. Artorias is a combination of the penetrator and king allant from demons souls. Lautrec was a toned down yurt. The crestfallen warrior is reused from demons souls and kings field 4. Patches appears all of the souls games apart from ds2. I could go on for quite a while.
I guess. They serve similar functions in some ways. Yurt is fairly different from Lautrec outside of "they do something to affect your homebase in a negative way." The level up maidens do for sure but I don't know how you could avoid them being reskins really.