To your point, the most recent gigantic d-bags to be drafted early/anointed, who come to my mind are Mayfield and Manziel.
Manziel never saw the sign for the "you're not that good, Son," detour. I doubt Mayfield will, either. And I don't think he'll be a great QB when it's all said and done.
Allen's got swagger, which I love. Mayfield doesn't have swagger. He's just a jerk.