I don't think there's any doubt about that.
From a pure numbers and production standpoint it's probably the worst in history without even factoring in all the accusations against him and everything Cleveland gave up to bring him in. The latter part just takes it to a whole new level of awful.
I doubt a sports contract will ever top his in terms of awfulness. The stars truly aligned for it.
Was Mahomes the front runner?
I mean it's not like he's having an especially great seasons. He's on pace to have the fewest TDs and yards with the most INTs of his career. In fact I'd say he's having a slightly worse season than Dak Prescott who don't think is playing at an MVP caliber.