But this has always been the case.
It's weird that people are treating this as some new situation, when it's really the same exact duality as always.
In ANY given fixed spec device, you can always do a certain amount more at 30fps than 60fps. This is a rule that exists no matter what hardware we're talking about.
I also think it's ridiculous how people think 'reconstruction' = 60fps, when there's absolutely no reason for such an assumption. The way to really maximize the hardware is to do reconstruction + 30fps.
I'm assuming you know that reconstruction works because it accumulates (reconstructs) the data over X number of frames?
Let's say some game reconstructs an image based on 4 frames of data. That's 4/30th's of a second spent to accumulate the data. If you have fast motion you will easily be able to see artifacts introduced by this. At 60 FPS, 4 frames will only take up 2/30th's of a second leaving a much smaller window for any artifacts to accumulate or be visible.
Reconstruction is nothing new, there's been various forms of it for a long long time now. It's generally recognized that best results are at 60 FPS or more. Lower than that and artifacts when in motion due to temporal accumulation become too easily visible.
Sure, you can hide some of that with heavy use of full screen motion blur, but full screen motion blur isn't always desirable (I personally always disable it because it looks so bad and unnatural). And if you are using full screen motion blur to hide the temporal accumulation/reconstruction artifacts at 30 FPS, then you're already losing any detail that you've gained from going to 30 FPS by purposely blurring everything to hide the artifacts.
Using Control as an example, it looks OK-ish at 30 FPS with their motion blur, but looks significantly better at 60 FPS. Turn off motion blur and suddenly you have greater image fidelity, but also impossible to ignore reconstruction artifacts at 30 FPS. At 60 FPS it's better, but their reconstruction is so aggressive that it's still noticeable, albeit to a far lesser degree.
So, that's the trade-off for reconstruction at 30 FPS. When standing still, you have good IQ. When in motion you either have loss of detail due to blurring from motion blur or very visible artifacts. You can, of course, have less aggressive levels of reconstruction with lower potential increase in IQ, but also with less artifacts at lower frame rates, but those will still look better at 60 FPS even at reduced rendering quality.