[strken]

If your goal is to "obtain physical fitness," which as stated is a totally unquantified goal that could be defined in any way you want, then you are infinitely better off waving your arms around with a VR headset on than sitting on the couch.

The attitude of "well actually you're doing it all wrong and this is poorly optimised, watch me piss in your cornflakes" fails to take into account the merits of doing anything at all. Sure, they might plateau after a few months. That's not a problem. Anyone who plateaus is going to either A) decide they've made it far enough, which is their business, or B) find a way to push themselves, which will get them doing everything you're talking about.

What is your goal here? Get the excited people who like VR to stop exercising because they're not doing it efficiently enough for you? Why?