It seems the four-finger swipe gesture is hard-coded to the grid effect. Once the overview effect matures (or already?), it probably makes more sense to map the gesture to that effect. (I am actually surprised that gestures are not user-configurable.)
Desktop Grid and Overview give you a different UX for virtual desktop management, but I agree that this should be configurable. And I'd like Overview to get the gesture by default.
This has been done for Plasma 5.25!
Great! Looking forward to using it!