That is a fair point and a good question to ask also.
To me it looks likely that by now, if our tracking systems had exposed their supersonic weapons were not as fast as claimed, this would have been all over mainstream news by now. And heads would already be rolling on the Russian side for doing what the West is famous for, falsely "bigging things up" , putting on a show which just becomes embarrassing when it's seen to be all hot air, like a 300 second starship firework.