If you look at the team metrics under Hakstol and Gordon, they're worse under Gordon except for shooting % on the PP and save % at both 5x5 and the PK. The PP sh% is probably an anomaly, just like the historically poor PP sh% before he took over - like BABIP it tends to regress to the mean over time.
Hart came up and Elliott came back under Gordon, while before then, the Flyers easily had the worst goaltenders in the league.
Flyers under Gordon are more turnover prone, struggle to get the puck out of the D-zone and tend to make too many stretch passes instead of moving the puck up the ice.
With Hart as the starter (amazing game against the Pens), a veteran backup, goalie should be set (and a bunch of good young goalies that are 2-3 years away in Sandstrom, Ersson, Ustimenko and Fedotov).
Fletcher has a lot of assets to play with this offseason, from cap room to pick #12-15 to some young players he can deal.