1. Ok yeah proclaiming him as the undisputed greatest is a bit OTT. He is closer than you give him credit though! His impact on hip-hop music in the 90s can't be overstated.
2. He has at least 3 top class albums, come on
... Me Against the World, All Eyes on Me (one of the better double LPs) and Makaveli are all up there in terms of quality. That's not bad for someone who died in their 20s. I mean, Biggie is considered the GOAT by some and he only had 2 albums!
3. A lot of stuff from that time sounds dated... And not just in terms of production. I dare you to listen to Efil4zaggin again with a straight face at all the misogyny... I try not to let that impact my understanding of a project's overall standing in the pantheon.
But overall fair enough, I don't think he's the GOAT.