There is nothing concerning about it. As others have pointed out, getting proper coaching at the NHL level is also getting rid of bad habits. Kakko could still rule Liga with those habits. But as his rookie demonstrated, it is all but impossible at the NHL level as he was a turnover machine.
There is NO coach on ANY team that is going to allow an 18 or 19 year old to continue to play the way that they did in Finland or Canadian juniors. Period.
This place has become ridiculous.
HF: "I know that Kakko's play has improved"
HF: "Is his development being impacted?"
Let's go to the video tape. Chytil comes to camp as an 18 year old. Gets sent to Hartford. Listens to what the coaching staff told him to do, knocks his own door down and plays well. Enter this year, prior to injury appeared to be thriving. Kravstov comes into camp as a 20 year old. Has less than inspiring play. Gets sent to Harford, pouts and runs home to Russia where his play suffers. But, has conversations with management and coaches, gets his head out of his tukhus and turns his game around the following season to a degree that puts him squarely back on the radar. Andersson, comes to camp, makes the team, plays mediocre. Next year, at 20 years old, comes to camp and is sent to Harford. Decides that Harford is beneath him and runs home to Sweden. Starts to send out weird tweets. Has conversations with management and winds up being traded to LA where he is promptly scratch in 3 of 11 games, and has 1 point in the other 8. All the while averaging 11:25 of time. Clearly the LA coaching staff is impacting his development the way that the Rangers did.