I think we're underrating coaching in this equation though. Darnold has been given a coach killer who deconstructs his roster, fails to protect his QB, and throws his roster under the bus. Rosen's situation is just too bizarre to even want to account. Even Mayfield was written off by many after last year due to a bad coach.
I look at Darnold, Jones, Rosen, Trubisky, and other young QBs and of course we can say they didn't or aren't succeeding in their current situations, but I can also see some pretty clear ways in which their respective organizations gave a young QB chicken **** to try and overcome. Staffs and organizations don't want to bother building a team anymore. They want to have a young QB that can transcend all their organizational problems, even if that's unreasonable to expect of a young QB, and if a guy can't right away they don't get an extended opportunity to have things improve around them.