I am pleased to have discovered your fine web site, and FitzQuake referred to in https://www.quaddicted.com/engines/software_vs_glquake. For more than a decade I’ve been playing GLQuake, and consider that a reference. I can see the problems with light contrast outlined. The dozens upon dozens of mods that every classic game has spawned today are confusing. I’ll admit that FitzQuake is subtly better all round and not worse in any aspect, including compatibility with old systems. Great work.
My 2¢ regarding the point about “conversion to pixelquake”. I quite like Nvidia’s Sparse Grid Supersampling. It seems to be applicable to nearly every game, both modern and old. With it, I can get pixels up close where they are missing, and stable, filtered picture in the distance with a smooth transition between these extremes. Best of both worlds.
I was playing with Half-Life the other day and accidentally discovered this. The setting in control panel is called “Antialiasing - Transparency: 8x (supersample)” It seems to affect all textures under OpenGL, not just “transparent”.
GL_NEAREST_MIPMAP_LINEAR with supersampling:
The HUD not pictured remains sharp exactly 2x upscaled.