I'm not going to use the word "goat" because I don't really believe in that, but IMO what separates a good rapper from a great rapper is how determined you are to find the production/producer that brings out the best in your sound. The whole is always greater than the sum in music... A mismatched beat doesn't just drag down a good verse/song, it brings the rapper's understanding of their own sound into question. The same is true of mismatched hooks and flows... Great rappers have an ear for when the music accentuates their vocals and vice versa.
The best rappers IMO tend to be musically well rounded... They don't limit themselves to one sound but at the same time they know whether their sound is going to compliment the music or not. Lyricism and everything else comes after that IMO... There's a lot of lyricists who are just as likely to make a shytty song as they are a good one because they never conceptualized their own sound. The lucky ones bump into producers who do that for them.