Inevitable Job Simplifications?

[Lyth]

Movement is tied to not dying. Square cannot or will not increase the skill-floor before Extreme and players don't want that content to be more difficult.

This is incorrect.

Positioning and movement are related to uptime. Plenty of fights at all difficulty levels offer you choices between playing safely and moving off the boss or playing more aggressively to maintain uptime. The main differentiator between players often isn't that you forgot what button comes after Hakaze, but that you lost a GCD or two by playing a bit safer than you actually needed to. Having more interesting movement tools available to the player also means that you have greater room to challenge players with this. That and designing less fights with arena-wide hitboxes and wall bosses.

I personally don't care much about movement. I care more about positioning

These two are functionally the same thing. It's about your spatial position on the map. Otherwise we'd be playing a text-based game with combo buttons.