Reading through the comments it seems a number of issues have been identified to explain Pettersson's current play. Last year is was that he didn't have adequate wingers. This year he isn't playing with Hughes. Or, he must be injured. or it's the Coach's system, or it's fans being too hard on him etc.
To me it seems that the reasons for his lack of being "1st year Petey" are bigger than any one single factor. While all of these factors contribute somewhat to production/performance, none explain his apparent disinterest. I say apparent because I honestly don't think he's trying to sluff off but that's certainly what it looks like. To me the bigger issue seems to be between the ears. You don't get a guy who has clearly shown an elite skill level and an ability to drive play suddenly losing that ability for an extended period (now going on 12 months).
If he really is who we thought he could become, the system and who he's playing with should not cause him to disappear for games or stretches of games only to show flashes.
The only forwards that are currently earning more than Pettersson are Matthews, McDavid, McKinnon, and Panarin. And therein lies the biggest issue. Expectations are based in large part on salary. At his current playing level he is a valuable, productive, player. He just can't be expected to be on that list with those players. I still hope, even believe, that he will become that player that drives play, that makes other players on his line look like stars rather than needing other players to make him a star. Who knows where this is going