If the sub was too good, his audience would look forward to Rush's absence.
For example, take Walter Williams. I know he's not everyone's favorite, but I hate to miss the show when he's subbing. Conversely, I only tune in to hear Rush once or twice a week.
Maybe I'd tune in consistently if Rush himself was on the air only as often as Williams is. But, I always look forward to hearing Walter Williams.
Rush seems to be obsessed with body parts and bodily functions lately.