Sheahan has been on the ice for 623:58 this season 5v5. he has spent 159:27 with Guentzel and Kessel together. That's 25%. not 56%. And that's not the wing combo he has looked worst with. I watch hockey you know. He has played just a quarter of his season with those two but it has accounted for more than half of the on ice production.
He's not wrong there. Guentzel - Sheahan - Kessel as a trio look terrible together. I think that's mainly due to Guentzel on LW (something that doesn't really work anywhere with Kessel, when looking at actual GF/GA). But it's also due to stylistic reasons, just RS/PK are probably not ideal fits. They might make it work better with another LW... but who knows. Sheahan at his core is a non shooting, defensive center. That's just his game. He can change it a little (and it's much improved since he came to PIT), but odds are he will not stray too far from that. Sodo is simply put a better offensive player then he is. He's not as good in the circle, and I don't think he's as good defensively (that says more about RS then Sodo), but I'm not sure how anyone can say RS is better offensively.