Thanks for the new Proton release including your fix (didn't realize you are
the release manager :) ). As far as I can judge until now, the result is good
enough in practice. There is this this reproducible spike, but moving the
camera while in game seems free of stutter (a bit hard to judge, since the game
is very stuttery in general).

It's definitely not the only case where atomic modesetting is hypersensitive, I
wouldn't be surprised if it required some kind of rather comprehensive
restructuring to make it more resilient in general.
E.g. there is still this aforementioned problem with gamma adjustments:
https://bugs.freedesktop.org/show_bug.cgi?id=108917

And there is also weak stutter each time when other windows on Xorg receive
focus.

All those issues where non-existent with old legacy DC (amdgpu.dc=0 on Polaris
and older). Intel probably is affected the same.