I don't think Skelton is "stupid," but he left much to be desired as a professional quarterback. I like his demeanor, toughness, and arm, but he does have the penchant for locking onto one receiver, and even though he has "superior pocket presence" that gets embellished, he still has trouble with accuracy. And accuracy is one of, if not, the most difficult skill to teach a quarterback in the NFL. Either you have it or you don't. Same reason why I don't think Ryan Lindley was worth a 6th round pick, even if it is a late-round selection.
Skelton should get credit for the game winning drives he executed, but more often than not, he put the defense in peculiar spots with some of his ill-timed interceptions during the course of a game.