I'd appreciate your points a little more if I knew you held them prior to 2015. Seems to be a little revisionist.
IMO, the Bills landed him because they paid the most, period. If you want to contend Mario is a mercenary over a locker room leader, I wouldn't disagree. Horrible teammate? That's going a little far. Mario also wasn't in a contract year, but it technically may have been as his cap hit was rising and a restructure/extension was necessary or he was going to be released.
He's a net positive to me. This team is better with Mario on it. Is his loss the worst thing ever? No. If I had to pick who we lost this offseason between him and Kyle Williams, it's him, no question. But there are hundreds of Mario's in the NFL. They are on winning teams and losing teams and everyone in between.
The "Mario question" is more of a media driven narrative than anything else. No one bats an eye when a WR (like our very own Sammy Watkins) quits on his routes. When he publicly complains about his targets and numbers, the excuse is that "he's right, getting Sammy more involved probably leads to more wins." Why can't the same be said about Mario? Why can't scheming to get Mario 15 sacks a year not also be said lead to more wins? The argument that the player is in the "right," would hold for Rex's scheme too, no? You yourself even admit that Rex messed up this season and the defense was bad.
Mario quitting is unacceptable. But there's a fine-line between Mario's antics and virtually the rest of the league, and he's hardly the only one to dance it.