I like this design.

But that’s just it: the core concept of Mare-dusa would be different from Storm King, fundamentally changing the dynamics in the movie.

For starters, instead of the stupid scene where the useless princesses with powers great enough to move heavenly bodies were subdued by a unicorn with a broken horn and a sack full of stone-bombs, we could’ve had a scene where a Stone Queen establishes herself as a legitimate threat by petrifying princesses and ponies with a mere glance.

Whereas the Mane 6, Twilight especially, felt severely nerfed when having to run and hide from, well, everything (like even those dime-a-dozen pirates were somehow too much, and it didn’t help that Spike’s flames were finally weaponized at the climax after a complete stranger suggests as much), at least in this case they would have to run and hide just to stay out of Mare-dusa’s vision.

It could even explain why, say, Discord couldn’t get involved and suddenly make the struggle one-sided with his reality-warping powers, or for that matter why the Mane 6 didn’t just go after the Elements of Harmony again instead of leaving Equestria for a new artifact, especially when Rainbow Power had only ever been used once and the movie would’ve been the perfect opportunity to bring that back. Passive Petrification en masse isn’t exactly the easiest thing to counter, especially if we’ve never even seen the highest levels of magic turn more than three characters to stone at once.

Just this one change of linking strong magic to the villain(ess)’s field of vision has ripple effects that change the dynamics of everything. Besides, with the tyrant ruling over all she surveys in the most literal way possible, it suddenly makes more sense that characters have to work in the dark and entire civilizations have to operate underground.

not necessarily, I mean if they utilized Mare-dusa the same that they used Storm King nothing much would’ve changed

The FiM movie would’ve worked a lot better with a Mare-dusa instead of a Storm King.

mare-dusa?