IMO, "systems" or "styles of play" have only a little bit to do with this.
He's playing against younger players in a league where there is a lot less parity than in college hockey. He'll obviously score a ton more points up there against youngsters on some crappy teams.
If that makes him feel better about himself, to see some higher numbers on his stat line, then I guess he got what he wanted by leaving.
That said, it's still shows an incredible lack of respect and maturity to bail on your teammates mid-season.