You can't strip down HL:Alyx to play outside of VR, or other games specifically designed around precision motion controls with total freedom of head movement. With PSVR 2 controllers the difference will only get bigger. Motion controls of course can also be used outside VR, however in 2D on a small screen, motion controls that rely on 3D placement just don't work very well.
Head tracking can also be the primary control input like with Eagle flight, there is simply no way you can be fast and precise enough with a stick to get through the speed challenges. Plus of course the whole getting a different perspective / looking behind things will be hard to replicate outside VR, Astrobot and Moss won't be the same. Also for on rail shooters, peripheral vision is the big advantage in VR. Your attention is automatically drawn to where the next action happens. Without VR you would have to scan side to side continually. Rush of Blood would be very hard outside VR.
However you can port non VR games to VR and enhance them. Skyrim works pretty well with dual controllers, dual casting, sword plus shield, bow all very fun to use in VR. Simple ports like RE7 and Borderlands 2 are functional as well. So more games could have VR modes, especially with foveated rendering baked into the console. PSVR 2 has eye tracking, with foveated rendering the required step down in fidelity should be a lot lower than it was on PS4. Also higher resolution means less work on getting all the UI elements readable.
Yes, the resolution. Wonder what they will go with since the last one was 2x720p.
Peripheral vision your right about, similar to playing racing games like GTS where you could look around, or even Star Wars Squadrons, but as we know both games work really well without VR too and still remain mainly non VR games. Which is why I think although it may be better with VR, don't mean it won't be great without it, it will simply lack that added depth.
Games like Moss and Astrobot simply wouldn't work without VR and would need to be redesigned. As always not everything worked be possible to translate over.