Not really development hell, but it's due to the network losing confidence on him after the failure of the Power Puff Girls movie.

If it wasn't for the cancellation of the Popeye movie, we couldn't have gotten season 5, as per his interview before S5 aired

Aside from Book 3 on Avatar, Greg Baldwin also voiced Spirit Iroh on the Legend of Korra Book 2. He sounded quite off there since he has more speaking lines there than the latter.