Galchenyuk is one of those players who'll be 37 and people will say "Man he has so much potential".
He's in his mid 20's, he is what he is, and he has a year left on his deal before MTL has to consider trading him, committing big money+term, or losing him for nothing to free agency. That's assuming Glachenyuk would even be open to staying in MTL with his relationship with coaches and his role throughout his time on the team being somewhat contentious.
So MTL basically gave up the traditional 1st+3rd+B prospect they probably would have gotten for Galchenyuk 1 year from now in exchange for Max Domi. Reading the main board thread, I seem to be in the extreme minority, but I don't think it's a bad move for MTL. It should be noted that career wise, their production is basically even, although Galchenyuk is more of a goal scorer.