At least Sullivan realizes he's not the defenseman that Vancouver has used him like. To be fair to Gudbranson, he was given pretty difficult minutes for a defenseman of his caliber. His quality of competition was higher than everyone on the Penguins defense sans Letang and Dumoulin, so maybe he can be less bad for you in a sheltered role. It's without a doubt that he has been used poorly, but bad results are bad results.
Maybe playing against easier competition gives him better results, but better than bad is still probably bad. I do think it's an interesting question for whether he'd be better than Johnson in the same role. I'm just hoping Gudbranson can perform like Engelland did for the Penguins back in the day, which is probably optimistic.