My bad. RBI and defense. If we're talking MVP, everything the player does matter. Simply asserting that a player has excelled in a particular area is, at best, an incomplete argument.
Leads the league in RBI + plays really good defense at 2B = MVP is still a weak argument in my book. Driving in runs and playing defense are definitely big parts of how a player produces value. But they're only part of the picture. And I'm not suggesting that you don't know that. I am suggesting that you don't seem to be accounting for those other things.