Think that's the way of Moyes and the like.
You have to get the kids time on the pitch or they will never be the best team unless they're wunderkind or you're completely out of options.
Football is about the next game because fans and chairmen will turn on a manager that overlooks the next game while building for the future. I suspect this is an area that we can exploit by building a young team, letting them play together and learn together and work towards the goal in a few years time. While the kids need steady older heads, we have them in Jags, Distin, Barry and the like.
I do not know Luke Garbutt, and you could be right that having a poor game against Downing would be a greater knock to his confidence than not being picked. I do know that I would be more upset to not be given the chance over a player nearing the end of his career out of position. That would absolutely make my head drop and make me think I'm not good enough.
As for the now vs later argument, I think that's an interesting topic in its own right.