Commentators aren't supposed to be cheerleaders, no matter who they played for. Everyone is entitled to their opinion on the Cowboys.
I literally do not understand why people get upset if a commentator of any kind doesn't share their world view when it comes to their football team or anything else of import. What Keyshawn Johnson or Troy Aikman or Michael Irvin or Stephen A. Smith or Skip Bayless or anyone else thinks (or plays the on-air role of thinking) about what took place this weekend doesn't matter. Develop your own opinion, and allow someone else to think otherwise.