I do not agree with that. Well, I agree that the best players can improvise better, but it’s based on LOTS AND LOTS OF PRACTICE and specifically, practicing situations they might encounter. So in the moment they may not “think” about it, but they are definitely prepared to know what to do.
Players like Bryant, Jordan, James, and Westbrook practice every combination of plays tirelessly, endlessly, to a Obsessive Compulsive standards of practice.
NYTimes did a great write up of this recently on Westbrook. And I think your predecessor Grantland did a piece on Kobe a few years back.