I mean that's kinda my point.
The way that the starts are designed limits the design space, because there aren't enough multiplicative scaling stats for AP to exclusively utilize.
AD can use CDR, atk spd, lifesteal, crit, and armor pen.
AP only has CDR and magic pen.
So while an AP champion might have some kind of mechanics in their kit which allow them to CC a target, they will never be able to out preform an AD champion in the same role, because the breadth of scaling stats AD has is larger, with AP mechanics being a subset of the AD mechanics. But AD has an equal depth in all of the roles as AP.
AP champions of a specified design are pretty much on par, in terms of scaling, to their AD counterparts as a result of the implicit auto attack scaling with AD.
This could be solved by either giving AP champions some kind of Magical Crit stat, but then that would basically homogenize the two stats even more than they already are. "which do you prefer, orange damage or purple damage?" kappa
The better alternative would be to add in some type of multiplicative scaling AP stat which allows AP champions the accessibility to equally scaling builds. Though in the MYMU they literally did the opposite of this by removing spell vamp, reducing the number of multiplicative AP stats to 2 from 3. Where AD, having been given better access to CDR over the past few years, is sitting at 4.
In fact, it'd be a lot of data mining, but I'd bet that the rise of AD's dominance in the game, corresponds with their access to a 4th multiplicative stat in the form of CDR itemization options.