Have you tried VR at 1080p? I understand your point (one number does not adequately represent "quality of experience") but for VR, 1080p is simply not enough due to the distance to the display (pixels are very visible).

I’ve tried it on even less than 1080 — a first generation iPhone SE (1136×640) in a one of those £30 plastic head-mounts.

Yes, you can see the pixels. But it’s easy enough to ignore that if the content is compelling.

FWIW, I own HP Reverb G2 (2160x2160 per eye - the highest I could find when I got it), and it's still not quite enough. 4K per eye might be what it takes.

The iPhone display takes up just a fraction of your field of view whereas a VR display covers most of it.

The difference is pixels per degree.