While I agree McCoy in his last season helped cover some of the crack that were forming and some of Mack’s weaknesses were always there, I’d argue that there is has been a noticeable decline over the years rather than simply just an end of good QB luck. Texas has had some great defenses over the last decade. While there were some mediocre years, there was nothing compared to how bad the current one is.
There were certainly ups and downs on offense, but they were all light years better than the 2010 team regardless of who the QB was. Chris Simms wasn’t loved but his team still won 11 games in his last season, with no help from another QB. Earlier Mack Brown teams also had much better running backs like Benson and Charles (Ricky Williams doesn’t count) that would have been good regardless of who was throwing the ball. The jury is still out on the young current backs, but the last running back that went to the NFL was Chris Ogbonnaya, a good but not great third down back, half a decade ago.