The Flyers have nobody to blame but themselves for not winning the division. If they could have managed even 1 win out of 3 games against the Devils in April they would have played the Rangers instead of the Sabres and probably would have swept them just as the Devils did.
Yeah, if the Flyers would have won 1 of those games against the Devils you would have won the division. However, that also means Jersey would have finished with 2 fewer points, putting them in the 6th seed behind the Rangers.
So you would've played the Devils first-round if you had beaten them one of those games.