Except, if you look at the actual facts, the only players that Prust fought that you could really describe as heavyweights in 2012-13 season are Mclaren and Lucic. Plus Finley for height and weight, but he's not all that great a fighter. The rest were guys around Prust's size who can hang with heavyweights like Brown and Neil and punks like Kaleta and Rinaldo.
Prust's fightcard that season looks much like any previous season, whether he played with a goon or not.
The fact that he's breaking down physically is nothing to do with how he was used in one season and everything to do with the style he's played through his whole career. If he's not healthy enough to do that anymore then the answer isn't to get a heavyweight to shelter him, it's to try to get rid of him because, quite frankly, Prust not able to play like Prust anymore isn't actually all that much use.