Both Prescott and Mayfield are good QBs for sure. They belong in the NFL and as starters.
But.... can they be CHAMPION starters? So far, the answer is no.

I'd actually give Mayfield more of the benefit of the doubt than Prescott. Mayfield has been part of the NFL version of the Three Stooges so that has been a huge handicap. Prescott is in a better organization, but imo, an organization that has been passed by, by a goodly part of the NFL. Dallas used to be innovative and bold. Now they just make the same mistakes over and over because they have the same 2 guys running everything. "America's Team" they are no longer. They are a little above middle of the pack at this point.

Put Mayfield in a good organization with strong direction like the Seahawks, and if he has the right mindset and takes to the coaching, he could do quite well for them. He's a far cry better and more dynamic than any QB currently on their roster. Besides, the way the Watson thing is going, maybe the Browns wouldn't mind Locke running the show for a year in a trade for would include Mayfield.