I already addressed this. Simply putting a cap on the extreme that infinite difficulty scaling can go won't stop anything. It will just convert things to speed runs. Sure, "everyone" could then theoretically reach the final difficulty, but it would come at the cost of many player simply getting bored of the the game being "too easy". And for what? So some players could reach the end with a sub-optimal spec?
This idea that everyone has to be able to finish everything is silly. If we're going down that road, then why not nerf Mythic raiding too? Make everything LFR so everyone and their dog can be free of having to get better at the game? And make no mistake, min-maxing is an aspect of getting better at the game. In some regards learning how to maximize your character, and use that min-maxing properly, is no different than learning a boss encounter.
The game provides different ranges of difficulty specifically in order to cater to different levels of skill and desire to min-max. The entire World-First Race is one gigantic celebration of min-maxing! Simply cutting the top end off the range of difficulty isn't going to help anything. And in some ways will actually make the game worse.