I guess it depends how one looks at "plenty" and their success rate. I'm by no means an encyclopedia of QBs and their past in the NFL but of the current starting QBs in NFL, how many had maturity issues? Of those current starting QBs, how many would you deem successful? Could a QB get away with maturity issues in prior decades with things like a developmental league, more practice time, grooming, etc... If a car is traveling 50 miles an hour from Chattanooga and Mariota is driving, would he still be able to hit a wide receiver in a tight window? What's Jeff George doing now?
As far as Winston being an "idiot" - I don't think I said that (might be conflating me with someone else) though I'm certainly concerned about his off field behavior and the uneven play on the field. What's with the uneven play in games? Seems like he's got a case of the "Schotty's."
Are you a big fan of his Jrry?