There’s some kind of secret-sauce that VD uses to host the VR apps, which appears to be significantly more efficient than Oculus’ native runtime that it uses with Link. Also, bugs specific to Oculus and Link don’t seem to affect Virtual Desktop, like the frame-sync problem that requires V-Sync to be set to ‘fast’ in the Nvidia driver settings. In short, I think the dev has created a stripped-down runtime and framecapture chain which works better than Oculus’ own, but it comes with limitations: it isn’t compatible with all VR apps, and it can’t use ASW at all.
Also, people using Link can get wildly different results, because there are many places to apply settings which can have a huge impact on performance. There’s the settings built into the Oculus app (refresh from 72 to 80 to 90Hz; and render resolution which confusingly varies its multplier value based on your hardware – e.g. a setting of 1.0 for you might not be the same resolution setting as 1.0 for another person!). Then you’ve got the settings that can be changed in the Oculus Debug Tool or Oculus Tray Tool (they both do the same things by the same means–one does not add to the other; they override each other) where render resolution can be further overridden, as well as bitrate, and supersampling (aka pixel density) on top of that which is not the same as render resolution though it’s somewhat related. And to really make things confusing, if you’re running apps in steamVR with Oculus Link (which is necessary for certain VR titles that don’t support the native Oculus runtime), it has an additional supersampling multiplier of its own, which can act on top of any of the settings I just listed above. And on top of that, steamVR has a ‘global’ setting for this that affects everything, as well as a per-app setting which multiplies the global setting!
So, that’s a lot of the reason people can have wildly different experiences. Add to the mix different hardware specs for each user, and you can quickly see that it’s quite hard to even match the same settings between users, much less match performance.
Lastly, MSFS does have a pretty glitchy/buggy VR implementation in general. I’m guessing it’s because it’s running via openXR, which is a newer protocol that Oculus only recently started supporting, and it seems to be nowhere near as stable and refined as their normal runtime.