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Well, if we're talking about the death of gangsta rap where "reputation" was more important than the music ("50 was shot 9 times bro!!!"), then Kanye was the one who brought the suburban element to the mainstream. Remember when his signature style was a pink polo with a popped collar and he was made fun of it for it? But the thing was that Kanye was never inauthentic about it. Like I said, his signature style was that he was suburban and not like the "hood" rappers. The inauthenticity came later when artists with a Kanye background pretended like they were 50.
If you're talking about poptimism in general, that's just a reaction to the over-pretentiousness of hipsters in the 2000s. But the pendulum always swings back and forth between "real" and "fake" being cool because fringe reactions become mainstream which cause fringe reactions, so we will care about authenticity in music again eventually. Probably not until 2020 though.