Did you select the runtime by running e.g. from Oculus software or from Steam VR? If you run steam vr from oculus software and then you select the game, which runtime does it use?
I had the Rift S for a couple of week before getting the Quest 2 and then refunding it. Generally the rift was easier to run, but i did not noticed performances difference, maybe i should have tested it more intensely. What i mostly noticed that made me sticking with the Quest is that the resolution was much more better. However, for the sake of the performances i have to keep it just slightly above the Rift resolution. (I have a 1080 Ti + 32GB RAM + Ryzen 3600)
Overall i’m not really happy with MSFS VR implementation, it is pretty tiring due to low performances and usually when flying you need to consult other tools. If it will manage to keep at least 40-45 fps i will be happier and it will be much more enjoinable.