To have this laundry list of negatives get a reply basically saying "yeah, it's bad, but we need to impress the stakeholders by forcing a Wayland default even if it doesn't work correctly" is baffling.
I use SDL so this hits a bit closer to home. Hopefully they can arrive at a conclusion that isn't harmful to us devs. It's already kind of a tossup whether it's even worth it to provide a native Linux build when Proton works so well anyway. I can't imagine this will help.
Interesting. I've been developing a game with SDL2 and think I know the stutter you're referencing. I passed it off as an oversight in my rendering code, but maybe it's as you say. Forcing Wayland does appear to work on my test machine, but integer scaling is broken. Might require some more tinkering or proper support in SDL3, but that's the only thing that didn't work OOTB, so not bad.