Do you know that currently the Pro has more native 4k games (current games) than XBX (announced) ? I am talking about games without dynamic resolution and checkerboard rendering.it doesn't look that bad with the same settings. As you pointed out there is some loss in detail and it's no magic and nothing out of the ordinary.
It is fake 4k. You are discussing the use of resources and while it uses less resources, it doesn't compensate for the loss of detail.
OneX : native 4k (2160p or 3840x2160) which is 8.294.400 pixels
PS4 Pro: 1920x2160, which is 2160 checkerboard = 4.147.200 pixels
what do you mean by that? Using SSAA on top of checkerboard wouldnt just blur the image somewhat? I don't think that method can be reliable to elucidate differences because if you go 5k-6k checkerboard supersampled you are just adding more inexistent detail in the first place.
There are plenty of games that will use fake 4K on XBX already.