@JoeRess I'm not sure I can speculate without running more games across more hardware (the latter is in very short supply these days). And under Wayland vs X11.
Just not optimized yet is one guess.
5% is impressive on the Steam Deck, but I wouldn't expect to see that drastic a performance hit on my laptop even if I was recording with OBS. Or with the Nvidia/AMD tools on Windows.
It's a curious issue. The kind I miss chasing :D
So I'm gonna go chase it.