The reason Nintendo may get too much credit for 60fps is because nearly all of Nintendo's output is 60fps with few exceptions. And that's why some felt it was a big deal when Mario Kart 8 was 59fps because it's "unlike" Nintendo to not achieve solid 60fps.
Again though, this is mostly a case of the genres that they commonly release being those that have 60fps as a popular framerate in all cases. You have Smash Bros, but that sits in the same bracket as something like Killer Instinct, Tekken, Street Fighter, etc. You have Mario Kart... and whilst I'll give credit here as non-sim racers often opt for 30fps, the first party's are still putting out Forzas, WipEouts (well, they were) and the like. 2D platforms are 60fps as a rule (Ori, Rayman, etc). Multiplayer focused shooters are 60fps as a rule (CoD, Halo, Battlefield, Overwatch and the mp portions of games like Gears and Uncharted).
When Nintendo creates more typical "experience" based games they do just as other people do. Zelda isn't 60fps for non-remakes, Metroid Primes weren't, Xenoblade isn't, Bayonetta 2 certainly doesn't quality for 60fps, etc... they just have less of these games than others do... but the platform also has less 60fps games, and the ones it has can generally be matched with an equivalent elsewhere.
It is 1920x1080 no matter if I accept it or not.
1080i 60hz is basically the same pixels as 1080P 30fps because instead of drawing 1920x1080 directly to the screen in 1 sequence it draw 1920x1080 to the screen with a odd & even field of 1920x540. the fields are separated by time but the 1920 x 1080 pixels still make it to the screen in the same time to make up a full frame.
Listen to yourself here...
Sure, 1080i at 60fps is the same pixel count as 1080p at 30fps... but it's NOT the same pixel count as 1080p at 60fps. So if you have a 60fps game like Dead or Alive 4 that outputs 1080i, it's not equivalent to 1920x1080/60fps... it'd be half that, in other words 1920x540/60fps.
You gone completely away from your "what the game buffer rendered" reasoning now, and have gone straight into "you realise it'll be 1080p as your output right?" territory. Guess what, 900p/60fps would be
greater in pixel count than 1080p/30fps, but surely you can see how silly an arguing point that would be right?
If we only care what the final image is made up of, then everything you play on a 1080p screen is 1920x1080, regardless of if it's checkboarded, native, or upscaled. You've rendered this talking point meaningless.
You can't ignore the ESRAM...
You pretty much can, unless the 320gb/s number is calculated with some sort of ESRAM of its own. It's the same bandwidth that a 980ti and a 1080 have, and higher than that of a 1070. There's no reason at all to assume a Scorpio wouldn't be able to native 4K any game that the XB1 can run at 1080p from what we know so far.