Indeed this is a valid point, thanks. On the X server applications will get touchpad gestures regardless of whether one is running Plasma or GNOME. However, workspace-wide gestures are not implemented in either on X yet.
On Wayland the display server is the one which handles workspace-wide gestures. Additionally, all events go through it to the applications. Perfect touchpad gesture support needs support in both. As far as I know Mutter (GNOME) handles both parts already and KWin (Plasma) currently handles neither.
Implementing touchpad gestures on Plasma would fall within this initiative, I will most likely work on that at some point in the future. Please vote in the poll so that we know this is important to you.
I'm not entirely sure if it's built into Plasma, but I remember having a (hacky, not with direct response) workspace switching gesture on Manjaro (Wayland, of course).
