i still don't agree with your point. a change of culture needs to come with a change of personnel. i've never seen a team of noteworthy poor defenders improve with a new coach at the helm.
regarding casey, he did wonders with dallas getting them to work in a strong system. i also think that people are giving both him too much credit and cuban not enough for changing the culture of that team. from top to bottom, they have strong defenders at every position. i think people are stuck on identifying that team with the soft mavericks of the past.