IMO, Rangers botched his situation. Rushed him, then put him in a position where he couldn't succeed. I (as well as a few Rangers posters) thought he had a really good training camp last year and was going to be utilized on the third line, but he started on the fourth line with Brett Howden and was sent down. Played less than 10 minutes a game. I don't think the frustrations necessarily show signs of immaturity. The World Juniors medal toss gets blown out of proportion.
Individually, he needs to play with faster players, but the Senators organization is building a roster with a lot of speed. Has he grabbed the bull by the horns? Nope. But, he is still just 21-years old, and if he is moved, which I think is increasingly more likely now that he is staying in Sweden, I think he plays with a chip on his shoulder for the next organization he goes to. I think this is one of those cases where it is both player and team.
Going to Ottawa would be a great situation for him. Longer timeline, less media scrutiny, and a roster that complements his strengths (he has a solid two-way game). HF will tell you he has "no value," but 21-year olds who need a change of scenery are always worth 2nd/3rd-round picks, especially to a team that has a treasure chest of picks the next two years.