I think “dropping like flies” is a bit of an overstatement when you regard the number of sorties being flown. I think this is more a sign of how saturated the airspace is with AA, if any pilot is just a bit uncareful or unlucky, they will get shot down.

Tbf. these have been more effective than I would have liked to see against Ukrainian armour, and we even have a video of one surviving having its tail shot off.

As for how they would do if western aircraft were in the air: That might be a different story, and not one I’m going to speculate about.