There are a litany of reasons why the Flyers are better this season and Sanheim getting first pair minutes, succeeding on his off side, with York providing a stable partner are absolutely contributing factors. Sanheim/York playing against the opposition's best line is a significant improvement over Provorov/Fit-of-the-week doing it.
Even with Couts, the Flyers only have three natural centres including Frost and Poehling. Take him out of the lineup and the Flyers are undoubtedly a playoff longshot, despite the positive impacts of Sanheim/York, Walker/Seeler, and the unexpected usage and positive contributions from Brink and Foerster.
The worrying part of this early season success is that management will have a difficult time sticking to their current message of thinking long term. It is extremely difficult to tell a winning team that you're either trading away positive impact players or that you'll do nothing to improve the on ice product without hurting morale. Briere has said the right things so far, but I'm highly skeptical he'll stick to his guns if the team is firmly in a playoff chase.