I really wouldn't know.
If he's suggesting that most mainstream rap is following a trend, that's how it's always been whether you liked the trend or not.
Name every sub genre of rap and I can name you 5 rap acts that did it similarly.Nah. Trends existed, but everyone didn't come out sounding the same to the same degree as you have it now. It's probably fair to say rap has been trending towards this, but you can't say it's always been like this. Mafioso rap was a trend, but every mafioso rapper wasn't using the same cadendce, refrain style, type of beats, ad libs, etc...
isaiah rashad still aint drop a follow up albumas head of a record label he can directly change this by releasing music that does not sound like what he is complaining about
so why not do that
Similar sounding beats, similar sounding flow and cadence. He’s not wrong.