I don't think Shelden lost his minutes to Big Baby. IIRC he started seeing less playing time and DNPs before BBD returned back from injury.
I don't know what made him get into Doc's doghouse but I liked him when he was playing. Those hands of stone were a killer but his rebounding was a plus. As the last big off the bench he is vastly better than what we had last year but with Sheed, BBD and even Scal before him I don't see him cracking the rotation anytime soon.