Mikami left Capcom Production Studio 4, in favor of Clover Studio, which is also owned by Capcom. It is where Kayima (DMC, RE2) and Inaba (Steel Battallion, VJ) both reside now. From what I hear, much of the talent at PS4 is also at Clover now.
And no, Shinji Mikami did not direct P.N.03. He served as the game's Producer. And no, Mikami is not one bit overrated. One of my favorite game designers out there.
And you have your story about RE4 wrong too Gaiden Is No Longer The Best...Mikami had nothing to do with RE4 until the last iteration, which is the one we now see on shelves. Kobayashi, the game's Producer, asked Mikami to step in and take over, after the previous director, couldn't take the game in a bold enough direction.