I disagree. Mahomes is a very special case. He sat behind one of the biggest class acts in the NFL in Alex Smith who apparently taught him everything as they went on, and learned from Andy Reid and Matt Nagy. 2 brilliant offensive coaches and 1 very smart veteran QB.
Allen does not have that luxury needless to say, nor do most rookie QBs when they come in the league.
Getting the player reps and letting them read the defences and learning from the mistakes is by far the best way to learn IMO.