Comics are generally not midwits; they have to be fairly intelligent. Rogan doesn’t seem to be dumb; he has excellent recall and can loop in a lot of different data points from previous interviews. But, he does tend to veer off into his areas of interest which are very speculative and offer no evidence. He also likes to create an air of uncertainty and wonder - perhaps that’s just the presenter in him. 

Also, we have to remember that he talks to people much smarter than him, which can naturally make him seem stupid - but really, we’d all look stupid next to them.