Did you know that Kid Cudi's song "Day 'N' Nite" has him singing in auto tune? It's not the T-Pain type, but it's still there.
And no, Kid Cudi is far from the best rapper alive. There are groups like Wu-Tang Clan, Run DMC, and Public Enemy whom are still alive. There are individual rappers like Nas, Rakim, KRS-One, etc., whom are also still alive.
So saying that a newcomer, like Kid Cudi, is the best rapper alive, is like a big middle finger to the true rap fans out there.