Being send down to develop your offensive game is linked to the confidence factor. When you play in a league where you're the go-to guy and you're leaned on to produce offensively, get PP minutes and play in the most important situations you gain confidence in your abilities of being a top player.
The reason scouts/teams often talk about sending players down is that they can dominate and gain confidence and in turn they are able to try more things to develop their game. For example make plays that your coach wouldn't allow you to make as an NHL rookie. It allows you to make more creative plays and develop that confidence in yourself to make those moves in games and eventually in the NHL.
On the other hand if a player goes straight to the NHL he will be more focused on not making mistakes, playing well defensively and eventually he will be more creative offensively after he settles those two factors.
Personally, I would send him back down to BU. He's got the strenght already, the defensive game is good, what he needs to develop is offense and creativity and developing that at the NHL level is a lot harder than it would be at BU.
