You can say Rakim had a "short" run or was relegated to the 80s or whatever you want. But the fact remains Rakim is one of the few rappers who there is an undeniable, unmistakable BEFORE and AFTER in regards to his reign. People rapped a certain way before him, and after him people rapped a different way. That alone makes him someone comparable to the absolute greats of other music genres. Miles Davis, John Coltrane...guys who changed their genre. Prince, David Bowie.
Being a pioneer is hard though, and doesn't guarantee you a spot at the top of lists IMO. Rakim is in my top 10 no doubt but I wouldn't put him in my top 5 personally. I mean there's certainly an argument for it, but for me personally he's not there.