Hey, I saw your post on r/emulation and decided show up. You are doing pretty nice job here. I have been busy with life lately, and have no time for this stuff. I'm happy someone is enjoying my work and keeping the torch lit, so to say.
About 1440p thing:
Yes, 199X and other presets were made on a single 1080p monitor and I have no idea how they are gonna look at other resolutions. Really bad I'd imagine.
About flattened colors/brightness thing:
As I've said I have only one monitor and it's pretty old at this point, so that must be the reason why it looks different. More over that, when working on 199X I wanted an even color space, but I guess my efforts just made it look gray-ish on other monitors.
About the rest:
You have to take into consideration that there is no one single perfect shader for everything. Well, maybe plain scanlines (but even then there are exceptions). 199X was made specifically for 2d games from Genesis and (S)NES, If it looks decent in 3d games - it is only a by-product of that. Honestly, I would not recommend using it in games with heavy dithering and low color palette. Silent Hill 1 and Metal Gear Solid look like hot garbage with 199X.
Anyway. You are doing well, keep it going.
PS. Your naming scheme is dope.