...couldn't we say about everything after, say, Jay/Nas/Eminem that all of these guys borrow blatantly from someone else?

Even Kanye West, the most individualistic alt-rap provocateur of the Bush and Obama years, is a direct descendant of Tribe and Outkast, no? In the mid-aughts Lil Wayne was undoubtedly a comet, but he still felt like a manic and drugged out Andre 3000 if you listened hard enough. I think after about 03, you'd be hard pressed to find a big rap star who doesn't wear his influences on his sleeves.

(In fact, Kendrick is so obviously better than Drake at being a whole artist, but I would entertain an argument that Drake/40's "sound" is something more unique than Kendrick's)