The Cowboys are better now than they were before Parcells got here. They are not better because of his coaching though. They are better because they have better talent. And now, they are underperforming for the talent level they have. That means they have poor coaching.
People want to say only losing by 1 pt. to Seattle in the playoffs is an evidence he's doing a good job, or at least not a poor one don't have a leg to stand on. The fact that they lost the game at all, and didn't win by at least 2 scores is a much better indication of how poor the coaching is. Seattle was not a very good team. Seattle severely weakened. Dallas had a LOT better talent than Seattle. That's poor coaching.