I don't hate kanye but I recognize the contributions he has made to hip hop, he's an average at best lyricist but an awesome producer that has always pushed boundaries instead of relying on cookie cutter hit making recipes...
hate if you want, but the fact is he sells records, to all genders, races in different countries to a vast age group that few hip hop artist can claim.
Mainstream? Sure that's what usually happens when you sell records, but don't forget he wasn't pushed or marketed until after he proved he can push records at an historical rate. No one even wanted to sign him to a record deal.