The reason why Yamal has reached so many games, it's not just because of Yamal, it's also related to Barca's current situation.
Even if Barca respects their academy, nowadays they had to take an approach where they have to risk it no matter what. This could end burning some kid? or getting them injured? yeap, it happened, can happen, but they have no other choice.
This is not a Barca with lots of International Stars in their prime and in the meantime making space with prudence to the new kids on the block. They are in the sort of situation like smaller clubs around the globe normally are and were, yet they still have the power and appeal to retain them.
It's a rebuild a la Pep, but not to cut some vices and re start, it's related to their financial and legal situation.
Pele and Maradona also started very young, but none of their clubs were or even are (in the case of Argentinos Jrs) huge clubs, so they had lots of minutes.
To make a parelelism between Diego and Aguero, Argentinos Jrs in those days could still hold to Diegofor some years, in Kun's case, Independiente lost him quite fast even if them are a way bigger club than Argentinos Jr.