The performance difference between the two systems is almost assuredly due to the input lag reduction afforded by monitors/tv's that are in Variable Refresh Reduction mode, regardless of resolution and screen refresh rates and whether the game is capped or uncapped at 60hz online, which it IS (and has been on both XBOX Series X and PS5).
And for the past year+, Xbox Series X has had VRR available online and offline for MLBTS 21/22. So the real performance gains should be seen when VRR is implemented for PS5 online.
To see the difference in input latency/lag, just look at the VRR columns in the RTTS input lag tests and you can see that the latency when using VRR is a whopping half of (or twice as fast) as the input lag of monitors/tv's in non-VRR mode.
https://www.rtings.com/tv/tests/inputs/input-lag
Take for example:
LG OLED C1 - 10.6ms (4K 60Hz) 5.6ms (4K VRR)
I anticipate that SDS will implement VRR into the online modes for PS5 now that the feature has been made available for them to do so, and all of the current hullaballoo over the feature will soon be forgotten.