Nobody had Patrick Mahomes going in the 1st round 2017 draft. He landed in a better situation than Josh Allen in regards to coaching and skill players around him. Josh Allen has the physical tools and smarts to be a good QB.
Andy Reid is one of the best QB developers in the game (Farve, Kolb, Foles, McNabb, Alex Smith) all had great seasons under Andy Reid. So I would not expect anything but goodness from Mahomes.
Josh Allen will get there, his road to the top is different.