None of the US Voice winners have had the sustained success that old Idol contestants still have.
Our version is even weaker, and with less chance of a breakout star.
I don't think there's anything wrong with the format (in terms of the chair turns). but it does rely too heavily on the egos of the judges (sorry, coaches), and often they steer their contestants into styles and genres they are uncomfortable with.
I reckon if you scratch the surface it's more than just "relying too heavily..." on, in fact it's all about the judges and their ego. It makes 'good' television which brings in ratings and the network / producers etc get their $$$ regardless of how the contestants perform post-show. Although, I don't think they'd like to admit it, I feel like they have no particular interest or care in creating a new star.