I think that quite a bit of failures happened with Miller.
Miller was obviously doled out his punishment, but the question comes back to whether or not he understands the severity of this. If this is considered "no big deal" to him and the letter writing was more for show, then yes, there should be a lot more time spent to change that direction.
I look at what sort of support system the player had around him. Upon the incident taking place, did the player and the support system treat it seriously? Family, counselors, doctors, teachers, coaches, even friends, to a degree.
I see this as someone who went and talked with a therapist or counselor, however, just going and talking does not necessarily mean progress has been made. Things like that can identify why a person may act that way, but until the person has an internal review of themselves with the guidance of working on those issues, there won't be something to fix until that person becomes engaged in fixing it.
I do believe that the support system (which includes hockey and coaching staffs) did not provide more of the guidance needed. If this exact attitude had been taken by the USHL, as a whole, then maybe the player would realize that this is the start to a potential future, and if not being able to play in the USHL is a part of the consequence, then he needs to act accordingly.
I think it is a case of someone who is willing to show responsibility, but it has to be on his terms. That is great for something you are good at, like a sport. That may not balance your responsibilities in other aspects of life. That is what got him to this point.
It definitely sucks that it reached this point as well, but if there were more clear efforts by programs to get him help, I think that come-uppance would be much more tangible and beneficial. Now, instead of support, he may move to a different country to play. Can't say for sure if that is the proper support needed.