I've got a bit of professional experience with the run flats on Lexus and Mercedes vehicles.
They are simply a safety feature and convenience, not a run forever tire. The idea is to be able to drive the car to a location where the tire can be replaced. They do ride rough and don't have the handling capacity of a performance tire. However, they make up for it by deleting the spare tire and then you've got that whole peace of mind when you do run over junk in the road.
Driving on the early run flats was like riding on stone wheels (or an Escalade with 26s). The latest versions are light years better but still don't quite feel like a Pilot Sport.