Well building is a key which usually has a value as well, like building=hospital. There is never just “building”.
But there are of course missing or wrong tagged objects.
The benefit of that approach is that everyone noticing wrong objects in the sim could fix the data in OSM and everyone would benefit from it, not just the sim.
Asobo would need to make sure that they update the data in MSFS from OSM regularly (not sure how often they do it now) and that’s it.