Sheed has definitely been disappointing. I don't have a problem with the volume of his shooting (he's the best scoring option on the bench), but his accuracy has been terrible.
After 4 consecutive seasons above 35% (and 10 straight seasons over 30%(, he's shooting 28.7% from deep. Rondo shot better than that last year. Coming at a time when he's taking them at an outrageous rate, this is a big problem for the C's.
His inability to hit open 3s has been one of the crucial factors in most of our close losses.
I like his defense for the most part (although he's ill-suited for the 4 spot at this stage of his career), his post scoring has been a boon, and his rebounding has been capable if not good. But 3-pt shooting was one of the primary reasons he was brought here, and 28.7% just doesn't cut it.