Are Mariota and Winston "can't miss" prospects?

If not, why should we be completely sold on drafting one of them over someone else?QB is the hardest position to learn than any other in the sports world. Both have shown that they have plenty to learn. Does anyone debate that? Is there upside so much more than any other player in the draft? Is there no player of better value? I am asking these questions legitimately. Everyone seems to think I am way off base in not wanting either QB with our first pick. Can anyone tell me why I should change my mind?