Dave's popularity sky-rocketed during the Chappelle Show, but he achieved demigod status after turning down $50m, for what appeared to be his unwillingness to c**n for pay.
That being said, while Dave is obviously funny, I never thought of him as the 'funniest'.
I don't think there is such a thing. I mean, everyone from Katt Williams, to Bill Burr, to Earthquake, Cedric The Entertainer, etc, etc, etc ... I've laughed hard as fuck at all of these people - repeatedly Shit, people say Kevin Hart ain't funny, but I've laughed hard as fuck at some of his shit as well.
I just watched some Deon Cole standup clips that were hilarious.
As for Bill Burr, I think he is great at taking controversial topics and not only finding the humor in them, but have a non-PC perspective that makes a lot of sense.