It's not Funk Flex's fault, but you're right about everything else. Flex has always tried to keep real hip-hop in the mix. He's brought all types of rappers to his Freestyle show which has helped careers. There was a brief period some years ago he even started a YouTube DJ mix show under Hot 97 where he would bring on pioneering DJs to do sets.
Hip-Hop radio in NYC doesn't have subgenres. In California, I believe they have a few stations that focus on or partly cater to older rap.
I assume NorCal stations play local rap heavily. New York has gone through so many scenes, subgenres and potential superstars since the 2000s but the mainstream never saw it because the radio never platformed them much or at all.