The former grid effect had darkened all virtual desktops by default, except for the one where you have hovered the mouse.
In case of a multi monitor setup, it had also removed the dimming of the corresponding virtual desktops on the other screens.

Since the QML based grid effect does not darken at all any VDs, this linking between two VDs on different screens, has been lost. It'd therefore be great to reintroduce it, not by darkening for sure, but eg by drawing an outline around the affected VDs.