I explained in quite a bit of detail in another post why I think that Cowen should not be in the NHL this year. I also explained that it was not just based on this one game.
As the next poster after you pointed out, his development is better served being the top dog in junior than playing 3rd line minutes in the NHL.
I suggest also that you review the stories of defencemen who were rushed into the league by poorly managed teams (see the Toronto Maple Leafs circa 1980-1989) and had their development hurt by being in over there heads. Names like Benning, Nylund, Iafrate would ring a bell with any knowledgeable hockey fan.
I'm glad too, but for different reasons.
There are plenty of busts out there when it comes to drafting... we've got a few to show for: Daigle, Lee (for all intents he's a bust), probably O'brien. However, to leave Cowen in juniors, even to dominate isn't going to help his development. He's big and he's fast, yes he needs more seasoning, but that seasoning needs to happen in the Pros. People said that Karlsson wasn't ready last season, I thought better of that and obviously so did the Senators staff. I'm certain our training staff knows whats best for a player, and to not stunt his development by rushing him.