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).
Using it cause fractional scaling on Wayland do some weird stuff with xwayland (reporting wrong resolution to software mostly), so using gamescope is the only way to bypass that bug and play at native resolution with scaling enabled.
Although it just stop working sometimes on my arch setup with 7900xtx. Right now it just spams errors in console and I have zero idea da fuck I need to do with that. Also, there a bug with closing game with gamescope: sometimes process will not close itself and stack multiple times in memory.