People change from being a child to being an adult, I don't know why that would have to be experienced so quickly and directly. How does anyone's entire life "play out"?Imagine that Sora, through all his struggles and nonsense, becomes the Master of Masters. How would that even play out? After his exploits in KW 2.0, he gets thrust into Yozora's world (or RINBO), faces some trials there then realizes that DARKNESS IS THE TRUE ENEMY? Does he then pull a Luke Skywalker and burn the old Keyblade Order down? No. That doesn't make sense. Can't suspend disbelief for that
I don't really want MoM to be Sora though (and it would kind of prevent a third saga from happening, if that's a thing) so, yknow, it doesn't really matter either way. Even if he somehow was I'm sure it would be much more complex than we are able to see from here.