Well, there's rap, and then there's bubblegum-rap. I think to what you are referring to is latter of those.
You hear those dudes singing "Girl, I wanna rock yo body," with the auto-tune? Yeah, that's bubblegum rap. It ain't even man enough to be considered R&B. Straight bubblegum.
But yeah, mainstream hiphop is going downhill. That's why you gotta stick to the underground.