You haven't proved Barrie isn't worth 5.5 million. You've just compared him to a defenceman who gets healthy scratched and plays borderline 3rd pairing minutes...
He was a healthy scratch a couple of times and it was a stupid decision/attempt to get him playing better. It wasn't because there was 3 defenseman on the Flyers playing better, let alone 6. You are making the statement as if he is some defenseman who can barely crack a lineup which isn't the case. Furthermore, over the last two years Ghost has produced at a higher PPG average and they are both offensive defenseman who will always be primarly judged on production and not defensive acumen.
Regardless, and in response to your first statement:
Tyson Barrie - 5.5 million
Morgan Rielly - 5.0 million
Shayne Gostisbehere - 4.5 million
John Klinberg - 4.25 million
Oskar Klefbom - 4.167 million
All four of those defenseman are younger than Barrie, as good or better, and are either similar players or bring some of the same qualities. All of them signed long term contracts either this year or last and are making less than Barrie for more years.
Yeah, Barrie is overpaid, proven.