That applies to some cases, not all. In the case of checkerboarding, I doubt it applies since the CPU is already used "efficiently" for the 1080p version of the games.
But if you are not checkerboarding and not gaining high resolutions you will know the GPU power is being wasted and I check digital foundry and other tech youtubers often and sadly that is the case in many ps4 pro titles.
If Microsoft can use that extra horsepower to achieve and resolve the issues of getting higher resolutions then we should see much better use of the console hardware. Both consoles where not designed to offer 60fps on 1080p because of their CPU bottlenecks and this extra memory is very important on the Scorpio because its one of the big reasons some games didn't achieve higher resolutions on the ps4 pro.
Just comparing it to a pc going for console-settings in 4k you will see they use more then 5.5gbs of total memory, usually they use around that just on the graphics card alone.
Its going to be a very interesting E3 for sure I am very excited to see if Microsoft has pulled it off but news like this does a lot to think they might have :)