The non-fullscreen (desktop) case uses an animation for the same purpose, locating the current app window in a sea of others.
So what would the preview be in the swipe-from-desktop case? A preview of the window-sea, or the desktop as is? What should the animation be? I suspect those questions are why they chose to just name the desktop.
I think it would be more consistent if the tab based preview only existed for the desktop window-sea and transitioned to the actual space previews when swiping between spaces.
Previews are also visible immediately if you set Mission Control as a hot-corner action. In never see the title-only spaces — i forgot it even did that until this discussion.
I also wish I could name the Spaces. "Desktop N" is pretty useless.
However, swiping beetween the previews, it sometimes jumps to random places in the order - which is not nice.
Possibly a bug, but I might as well just write this as a letter to Santa because it's got more chance of being read than a feeback.
The setting is "Automatically rearrange Spaces based on most recent use" which explains why the behaviour felt so intermittent.