Not most, but yes, overrated. Nash is most, because he rode his situation to the MVP twice.
Every few years the MVP suffers from the Boredom/"Surprise" vote, and since it's a media award and the media lvoes variety and storylines, yes, they give it to less deserving guys every so often. Not unique to Bastketball.
Happened to Nash too; not really at that level of player, especially if defense counts (which it does, turns out).