News Rumored 'Project Scarlett' Xbox Specifications: We're Not So Sure

From the one end, it’s weird that Microsoft might be releasing two next-generation consoles at once, only differing in performance.
Not really. As it is now, there are two different-performing versions of both the XBox One and the Playstation 4. If they go that route, I suspect it will be a similar scenario, with the high-end model targeting 4K gaming, and the more mid-range model targeting 1080p. Not everyone has a 4K display, and even if they do, they may not care enough about a moderately sharper image to pay a substantially higher price for it. The higher-end model having three times the graphics performance would be about right for achieving similar framerates on both models at their target resolutions. A game targeting 60fps at 4K on the 12TFlop model would also likely run at 60fps at 1080p on the 4TFlop model, much like how a 2080 Ti performs roughly similar at 4K as a 1650 SUPER does at 1080p. Forcing everyone to pay substantially more for a 4K-capable model whether they want it or not would be a bit like forcing everyone to pay extra for a Kinect, and I doubt they want to repeat that again. There could easily be hundreds of dollars separating the two variants, so it would make sense to offer both.