I don't think it's batsmen figuring him out. I saw him up close when he was warming up during the World Twenty20- I don't personally think it matters how many videos you've studied or how many times you've faced him, those variations surely can't be picked with enough confidence to play him from the hand. He just seems to have lost a bit of form, he's not getting any turn anymore and his accuracy has almost completely left him. It doesn't matter which way the ball's supposed to spin if it's not turning anyway. Being in and out of the team can't be helping matters either.
I can't see him being anything other than a huge success in county cricket, and I suspect the experience will do him a lot of good too. As for now, all we can do is await further developments.