As much as I love Flair, I think only three deserve to be in that top tier and that's Austin/Rock/Hogan. No wrestlers come close to the impact those 3 had on professional wrestling's relevancy.
I'd put Flair in the 2nd tier.
Heck, at this point, I'd probably even put Cena in the 2nd tier too. I mean like it or not, he's been the top guy for nearly a decade now and while he hasn't made wrestling as popular or huge as Austin, Hogan, and Rock did, he made a big enough impact to be considered a 2nd tier guy IMO.
You gotta think outside of a WWE/F perspective. Yeah, Austin/Rock/Hogan were big on a national level, but Flair was the biggest star going back to the territory days and thruout the ENTIRE South. And then when you consider he was better in the ring than Rock/Hogan, it's a no brainer