Why compare D:OS2 to Oblivion? It's like comparing apples and oranges. Total in-game territory of The Wicher 3, for example, is around of 136 km2 (without DLC's) and have more than 3000 characters (~526 has unique name). And this is only three regions which featured in the game : Novegrad, No Man's Land and part of Skellige Islands. Locations have small villages and huge populated towns. Overall the Witcher world is huge and much more bigger than regions of all the games combine.
Overall, I'm inclined to agreed. Also, I'm starting to believe that considering the tendency of all games in Divinity series, maybe D-world changing with each new game.