Kendrick is a conceptual rapper. He got some of the best concepts next to Lupe. He's clearly not the best at bars and sometimes (often) phones in his features or secondary projects but to say he can't rap is just being a contrarian.
For example his performances on the Black Panther album are lacking when it comes to meaning (sometimes it doesn't mean anything, like what he does on King's Dead) even though he does great hooks and flows well.
But for his main projects he's still very solid. I'd even argue that DAMN is better conceptually then TPAB.