Folks here are discussing the difference between AR and VR. My own take is that it's a difference of implementation. Quality VR with quality external cameras is going to give you a MUCH better experience than would AR glasses, and can of course do many things that VR glasses could not. I do think that AR glasses are much more practical and will have broader applicability. But perhaps not so much after a great VR impl…
VR is fail-deadly, AR is fail-safe by design and there's no way of getting around that. When VR fails, it's a black screen covering your head, whereas AR is the world around you. There are many circumstances where AR is far better than VR, even with perfect VR
I imagine you could use some tricks if you did AR with cameras pointing out and displayed them on a screen (this seems to be what the parent is implying), but you go back to "failure" being a black screen. In practice, I haven't seen this be a big deal. The display is black when it is off (like your phone assuming it doesn't put the screen to sleep). If any rendering misses a frame they distort the previous frame in the buffer to match any head movements (in AR likely reintegrate with new footage).