Have you tried it? I just installed gamescope and launched some games with it via steam launch options. So far I feel like the frame times are better. I use it on top of KDE and with an AMD card. Freesync in Gamescope works too. (Have it allways on in KDE if that matters).
I used this for a while, and while it worked great and much better than Steam streaming (never tried it with gamescope tho), the cursor doesn’t appear on Wayland, so I can’t play games using the mouse like EU4.
Which Wayland DE? Have you tried disabling hardware cursor? So for example in Sway/Hyprland or other wlroots based WMs that would be launching it with env:
WLR_NO_HARDWARE_CURSORS=1