As far as AJG goes, penalties weren't the problem with Zadorov at the end there. He actually cleaned that part of his game up a great deal. His continued inconsistency and glaringly bad defensive zone/PK defense is what did him in, and will continue to do so anywhere he goes in the NHL.
I don't agree that penalties were "part of his game." He was allowed to play his physical, in-your-face game, he just took insanely dumb penalties. Trying to start a fight with Blake Wheeler behind the play when your team is down, or shoving your hand into another player's face right when the ref is watching isn't being "tough," that's just being dumb as f***. Experienced "tough guys" and pests know how to skirt the rules better than that.
Greer and Zadorov just aren't that good. That's it. AJ will enjoy a decent career in the minors as an Alex Killorn-type secondary scorer with an edge...but at the NHL level he's a 12/13th forward at best.