I agree with this, except that I think Berube WANTS Brown to be a power forward and add the type of physical facet to his game that would allow him to function on the 4th line. I think Brown's most realistic path for an NHL career is to learn to use his size (and strength, which needs to increase) to play a lot more physically than he was doing in Ottawa. Then if he fails to earn a top 9 role (most likely outcome) he can play on the 4th line and have time to bring the skill of his game into his play. He'd slide up onto the 3rd line, get more minutes, etc. Eventually he could function as a power forward in the Top 9 and be a guy who is a 20 goal scorer a few times.
I don't believe he'll succeed at this. This is the path Berube seems to be outlining, to my view. But the alternate path is if Brown is good enough NOW to stick on the 3rd line. I just don't see it, and if he lacks physicality, even if he gets a spot he'll lose it later when he goes through a dry spell (and has nothing in his game to recommend itself when he's not scoring).
I know its easy to sit here and say he needs to learn to play with his size, and increased physicality. I harp on it because I think he has a coach in Berube that could really help him successfully put that all together, if he brings the determination and effort.