Jim Schwartz is a great DC. Rex Ryan is a great DC. They, however, run vastly different schemes.
This whole Mario issues is less about Mario (an aging and overpaid DE) and is more about the overall impact to the Bills decision to alter course with Ryan.
Many make the argument that the transition from Schwartz to Ryan cost the Bills a legitimate shot at the playoffs last season. Mario was the poster boy for the issues on defense, but remember that Dareus and Hughes combined for only 7 sacks last year. So the transition was not an easy one.
And the transition to Ryan's defense has also been pricey. It hastened Mario's departure, creating dead cap space. And the Bills spent their first 3 draft picks on the defensive front seven, which at the end of 2014 was unfathomable.
However, if the progress the defense is showing this season is legit (and like most Bills fans, I pray that it is), and the Bills make the playoffs, last season will be seen as an acceptable transition to success, and not a self-inflicted crash and burn season, adding many more seasons to the playoff drought.
So it's less about Mario, and more about the Pegula's decision to rebuild an area of strength under Ryan. Considering the results after the first 5 games, the argument tilts in favor of this decision.
If the team ends up at 500 or worse at the end of the season, however, the argument tilts back against the decision to hire Ryan, and Mario represents the missed opportunity to build on the success of Schwartz's defense.