Randomized studies are the gold standard, but it doesn't mean all research that isn't randomized is crap. They provide useful information as well. In fact, "gold standard" studies can be useless if they are flawed in other ways and that appears to be the argument of Dr. Risch.. He made some excellent points about the group selected for the study (and I wonder why the researchers didn't think of it). The average person is never going to suffer severe symptoms or be hospitalized for Covid, resulting in a dependent variable with almost no variation to measure.

I guess I am going to have to read these studies cited by Risch