I think you've participated in enough discussions here on LWN, including with myself, that actually explained what that meant. And I see you keep repeating this "question" as if it was never answered.
You know, stuff like this. Changing workspaces took one mouse click before and one view change (using GUI). Now it takes several, including a lot more mouse travel. Desktop visibility is zero, which was not the case before. The amount of pixels that change when working remotely using VNC has been significantly increased, which makes things even slower over poor links. It is practicality impossible to move items on the panel or define new panels using techniques available for at least two decades. Etc.
The _measurable_ stuff.
As I pointed out numerous times, Gnome 3 overview is essentially an implementation of RFC1925(6). That in itself is a regression, because everything is one step further away.
Unfortunately, nobody in Gnome development team is brave enough to acknowledge any of these facts. Instead, we are getting an Ultralite Gnome Classic, which just looks a bit like "classic", but it can't do most of the stuff that was possible before.