I appreciate the offer though~
But yeah, the TL;DR version is WebGPU is significantly faster, also optimized asf for newer mobile devices (or even some older ones with updated web rendering, w/e browser you use), The down side is, GLSL code wont work out of the box with it, apparently? Idk man, some jank sh* going down rn on PIXI's side lol, like they're improving which is amazing, but they've also made custom shaders obscure asf, I'll try deconstructing a built in shader and see if I can't figure out クソ何で makes them work~
Honestly it's pretty impressive. I'm a little behind the curve when it comes to what we can do now with web publishing and mobile play? I was blown outta the water when I figured out I can publish games that can be played in-browser exclusively. I need to do some more tweaking so that stuff works on mobile similarly, I wasn't really building for it and I wasn't aware that MV's default inclusion of two formats for all their audio assets was because one is for mobile (though that all makes more sense now, I guess it's an optimization thing). Just come from an era where RPG Maker made .exes and that's it XD
Reverse engineering from an existing shader is probably the way to go, I'd imagine. Especially if it's getting as janky as you say. I got the impression somewhere that mobile optimization is being prioritized, so it would make sense to me if they dropped the flexibility to use GLSL for more efficiency? Though I don't really know enough to say how much chunkiness you strip out dropping that support, hmm.
It is indeed quite impressive, as for MV/MZ while they are fantastic, every export no matter the device will export to a web format, on PC it uses NW.js (node webkit), like CrossCode does, this makes games easier to hack and even flat out edit, though to be 100% honest, no game is safe from that regardless of the engine lol.
As for reverse engineering the shader, turns out now you need to link your own gl program it looks like, and store the frag/vert shaders in an object, I just need to figure out why/how a glProgram is now required and how to tie that to the renderer, gonna attempt to just bootleg it and use the main app's glProgram