My disagreement with your take is because you said player, not QB. There's a long list of overrated players; Jim Kelly is not even close to being on this list at all!
As for being overrated as a QB, I don't agree either, but more plausible. He did have some elite talent, but he didn't let his ego get in the way, which he had a big one, by refusing to get a run game established.
My biggest critique of Dan Marino is he just refused to let his RB's establish themselves, his ego got in the way IMO. He had some good running backs, not Thurman, but good. That's the main reason the Dolphins couldn't get past the Bills to a SB.