His impact made it more mainstream within hip hop itself. Most of the names you listed were never headline artists. Most of the names you listed never had the ear of pop culture. Some of them barely had the ear of hip hop fans...and yes, I'm including those who don't dig in the crates like some do here...because that's most of the people who listen to rap and hip hop. The mainstream listener.
So, they may have done many things first, but how many people, IN THE MAINSTREAM, associate those things with a Cannibus or Del the Funkee Homosapien? And by the way, who the f#ck is that anyway? My point exactly.
I don't mean to take away what they did and give to Kanye. No, read what I'm saying. I am saying that Kanye took those bits and pieces as a listener and had a much bigger impact in terms of his career and his impact on pop culture in general as an artist.
Not much different than Jay saying "you made it a hot line, I made it a hot song."
Peace