Jay-Z is the Kobe of rap
I hate to say it because Kobe is my GOAT.
Kobe built his career in a big market in LA. Jay built his career in New York. As a result, they both have large, dedicated fanbases who proclaim them as the GOAT. They took from their predecessors (Biggie/Jordan) and incorporated it into their own style. Both have amazing longevity with memorable moments/hits but they are continuously disrespected by purists online. Both also debuted and left the game around the same time.