To be fair thats not quite true. The new drivers for the 300 series work fine with the 200 series by just modifying the inf.
People are reporting 10 fps more in Witcher with their 290x cards which is a 20% gain.
I cant see any reason why these couldnt have been released as beta for the 200 series now.
I'm not so sure, i think this is just a situation that's game related.
In this link they proved the 390x clock for clock is the same http://www.hardocp.com/article/2015/06/18/msi_r9_390x_gaming_8g_video_card_review/9#.VYM5uEZiMvx