Any QB will probably benefit from not playing in year one. Coaching, learning how to watch gamefilm etc is obviously helpful. At some point you have to play. You’re just not giving individual talent enough credit here. Smith with years of experience was unable to come close to Mahomes performance with largely the same cast. Some players are good and others are just great, at a completely different level. I doubt Josh Allen would be doing a Mahomes impression if he were in KC and sat a year. Four or five extra games sitting on the bench didn’t make Mahomes what he is today.