I think one of the biggest problems today's rappers have is as simple as this: they don't have good voices. Whether it being a unique voice or a powerful voice, or just plain sound good. Like, this is music. You don't need to sing, but if your voice isn't good, sorry by default you're not gonna be a great. Dudes like Method Man, Busta Rhymes, Nas, Jay-Z Black Thought all have either unique voices or powerful voices. Today's rappers all sound like Big Sean and Lil Wayne. A bunch of little punks. I'm exaggerating, but you don't have dudes like Method Man or Biggie.
That's why when I first heard Tyler the Creator's Yonkers, I was like finally, someone who sounds different and good. I'm not even a fan of the dude overall, but he sounded like a hip hop vet on that track, like he been in the game for over a decade.
The other thing today's rappers don't have his mic presence and charisma. But that's been the theme of the 00s. Most of these rappers too scared to look corny so they play it safe and release boring ass material and have boring personalities.They're either tame backpack/conscious rappers, wayne/drake knockoffs, violent trap rappers or drill rappers. Or rapping like Future lol.
OP I know we disagree on Kendrick, so I won't get into it too much, but partly why I think he's one of the only great rappers right now is because he's confident and does stuff other rappers would be too self-conscious to do.