You've not taken into account 3 things:
1) The Pro is capable of more than 1440p in many AAA titles. While it has been a common launch target, we've already seen several titles go a good amount further. The Scorpio will often be jump from resolutions like 1800p on the Pro, not just 1440p.
2) Outside of knowing it's 6TF, the Scorpio's GPU is a mystery. Until we know more about it, you can't state linear comparisons with the Pro as fact. It might turn out that linear comparisons are fine, or it might be that the Scorpios' TFs are worth more than the Pro's.
3) Many X1 exclusives already run at 1080p, since MS was willing to reduce their graphical quality (relative to what would be possible on the PS4) in favour of a cleaner image. It would be incredibly surprising if most (if not all) of those games don't run at a native 4k. Even your math would make that the case.
If you had said 'the Scorpio will not do a native 4k in all games', i'd agree. I think it's incredibly unlikely the Scorpio will offer a native 4k as a universal standard. I do, however, think it will deliver native 4k titles with at least a moderate degree of consistency. It's maybe even be it's standard (in a similar fashion that 1080p is the PS4's), but that'll depend on currently unknown variables.
