I find his situation fascinating because he actually started out looking like a good forward who may progress into elite offensive territory in his first season. It was still debatable he might not have all the tools for it but it was certainly looking that way.
Then he declined with every season going forward it seems.
Season 1 was a lockout season I believe?:
2012-13 Nizhnekamsk Neftekhimik KHL 22gp 10g 8a 18pts 33PIM -4
2012-13 Edmonton Oilers NHL 48gp 17g 14a 31pts 24PIM -4
Pace of close to 30g, 25as in his first season, on an abysmal team. Even had almost PPG in KHL. Was only -4 on a truly awful team so, no alarm bells just yet.
Then:
2013-14 Edmonton Oilers NHL 63gp 11g 13a 24pts 36PIM -33
Horrible team, big time minus, very low points, bad coach and sophomore season, no serious alarm bells yet but definitely unexpected.
2014-15 Edmonton Oilers NHL 81gp 14g 19a 33pts 18PIM -35
Alarm bells, same situation but no reasonable improvement, only 3 more goals and 6 more assists in nearly 20 more gp. Again, a huge minus and I didn't check but I'd be willing to bet even comparatively with teammates on a bad team, he was a massive minus.
2015-16 Edmonton Oilers NHL 60gp 8g 15a 23pts 24PIM -16
Essentially 3rd straight season of same performance, which is bad performance, aside from being a less bad minus, but even then the team likely did improve a bit and coaching changed iirc. Massive alarm bells at this point.
2016-17 St. Louis Blues NHL 40gp 3g 6a 9pts 14PIM -3
New team that albeit had no faith in him, producing at less than 0.25ppg for a guy expected to be a skill player, truly unacceptable performance.
All this to say, I do think given the serious production loss after season 1, Edmonton played their part in ruining his career. At the end of the day though, he's also had a chance to bounce back elsewhere and honestly it is up to the player to face adversity head on and improve anyway they can. He has the natural raw talent, but his style of play isn't great for NA hockey so he either needed to become a top 10 offensive winger or learn to play better defensively. I believe this focus is what caused his downfall.
More than likely, coaches and management told him to smarten up on his two-way play but he simply doesn't have the tools to manage being good offensively as well as defensively. If he finds a team that nurtures his offense and can recover from his defensive lapses, I think he can improve greatly still. Imagine him getting the opportunity to play with Geno, if he signs for 1yr 800k it could work and revitalize his career.
All this being said, I believe the org and him are both to blame, and I think his lack of offense while trying to play better all around got in his head, a lot of it is probably psychological.