I think it's a more interesting feature this way, and there is potential in certain pro apps to offer the ipad up as a touchscreen controller with deep hooks into the OS like a keyboard (or, more similarly, like a gaming keyboard) vs just a second screen. Or even offered as a permanent widget interface for MacOS as a 'focus' mode, with the assumption that it's kept near the keyboard on docked laptops/desktops. Display the Mac's app folder there, or split screen notification center with whatever pro app is offering an enhanced touch interface on sidecar.

So I hope they go the opposite way and figure this out as a more robust but ipad-focused feature.