Wholly responsible? That only applies to very few games (Undertale, for one), none of which were made by Obsidian or Black Isle. Not to mention metacritic user scores can easily be manipulated, Steam user reviews are much more accurate, and PST isn't even available there.
Also, Sawyer never had, in any of these games, a bigger role in the game's content than MCA did in PST and KotOR II. The closest thing for Sawyer was Honest Hearts. Speaking of which..
Steam user reviews for the FNV add-ons:
Dead Money: 61% (MCA)
Lonesome Road: 87% (MCA)
Old World Blues: 95% (MCA)
Honest Hearts: 83% (Sawyer)
The FNV DLCs are a better comparison between the two, as it's the same game with the same systems, same development cycle, same budget (only one of them was very limited IIRC), etc.