I have a similar setup to him, and it seems that what the latest beta version has done is introduce a bug that locks the frame rate to 72hz, irrespective of whether its set to 80 or 90hz, so it gives ASW a slightly easier target of 36fps to hit. In many scenarios with the rift s, it struggles to hold 40fps for the reprojection to 80 hz so can be a little juddery, if it cant hold 40fps, it often drops down and locks to 26 fps which doesnt seem as smooth. With a 3090 and top end cpu, you can maintain 36fps in most scenarios so the experience appears smoother. I think Oculus inadvertently locked the quest 2 into the sweet spot for flightsim with the most powerful setups. I have a ryzen 5900x and at low level in vr, im CPU bound to 40fps, with fairly constant drops just below - which causes the stuttering. With a 3090 you can crank the settings and resolution by quite a surprising amount before you become GPU bound if you are only going for 36fps.
If the DX12 update can improve the CPU performance just a little to make 40 or 45fps more consistent, it will transform the experience.