I’ve never had this as an issue with KDE. Do you have the command for prime render offloading on the Steam launch options? I usually launch my games through Lutris and it handles that pretty well.
The one the Gnome team is working on right now, as described here.
The basic premise of rearranging windows at an optimal size, without stretching them out to fill fractions of the screen, seems like the perfect medium between floating and tiling.