From someone whose been a Gucci fan since 2004, I would say he's an ATL rap legend because I haven't seen anyone more influential than him in the past decade. Classic mix tapes, classic fukkery, and a work ethic like no other.
As far as rap overall though, fukk no he ain't a legend....granted he stays in his lane and does it very well, but he hasn't dropped a defining album such as Trap Muzik, TM101, Deeper Than Rap, etc. If he can somehow drop that one defining album I think he can be considered a true rap legend but until then, I can't say that he is