Well, it turns out that compatibility with older games isn't a walk in the park, so pre-existing Xbox One titles default to a different set-up. In effect, half of the render back-end hardware is disabled and pixel and vertex shaders are each hived off to half of the 40 available compute units. It's a somewhat gross generalisation, but you could say that older games effectively get access to 3TF of power compared to the 1.31TF in the older Xbox One, and compared further to the 6TF accessible via the July XDK. As the improvements in render time demonstrate, pre-existing titles should get enough extra horsepower to max dynamic resolution titles and ramp up anisotropic filtering. Other back-compat enhancements promised by Microsoft - improved loading times, faster CPU power, RAM cache etc - are not GPU dependent so out of the scope of these metrics but there's no reason to believe that they will not be delivered.
In this sense, Microsoft's implementation for compatibility - halving GPU resources, effectively - may also explain PS4 Pro's boost mode, where only the clock-speed increase seems to make any difference in purely GPU-bound scenarios. Perhaps a similar utilisation of the expanded GPU was in place there - the difference being that even with the same limitations, Xbox One X has the advantage of many more compute units, plus a much higher clock.