I'm not saying the Flyers are the superior team to the Islanders. I just don't see this series ending in five games. I see Philadelphia extending the series to at least six games.
The Flyers won Game 2 and then lost 3-1 and 3-2 during the last two games. Philadelphia has proven resilient all season. The Flyers are 40-18 when playing on one day's rest and until Game 4 had bounced back from every postseason defeat with a victory. 
The Flyers dominated the second period of Game 4 and outshot the Islanders in that contest, 38-33.