Eddie Murphy entire comedy career is off the strength of just two comedy specials. Raw and Delirious. Thats it.
Kevin harts mistake is that he did 7 specials and still going. hard to stay funny for that long. If he had stopped at grown little man, no one would be saying his standup is bad. Every time somebody quotes the jokes he did that they like, its from his first two specials.
I don't think there is any comedian out there who got great reviews for their 5th or 6th comedy special. Should just stick to touring untelevized venues after you get those first few major specials.