What?
How do you know it was fully procedurally generated before??
Also they have built some very cool systems for this game. It's a proper step forward in a lot of ways. Brand new quest design/ exploration design. Obviously not perfect, need some work.
I did finish both Skyrim and Witcher 3 back to back before starting this. Difference is the same. Story driven vs system driven design.
Just look at skill tree in Skyrim, way more mature and full fledged. Witcher 3 is way simpler game with graphics/ music/ characters doing heavy lifting. Skyrim is all about simulation elements, how you can interact with them and do a lot of cool things.