But with the Vision Pro there is zero latency and the possibility of having many big screens, whilst when remote-desktoping into a Mac from an iPad you gain nothing and the high latency makes it worse.
Because it's not remote, if you are streaming from your Mac, it's right there, at 2m at most. It's much different than remote connecting from an iPad 100 km away.
It wouldn't, but why would you use an iPad as your main screen if you are near a Mac? It's just a screen, it doesn't bring anything special like the Vision Pro would.
It's using local Wifi (or USB), so the latency is very low.