Will Dirk Nowitski have a better legacy than Malone and Barkley if he plays at this level for 3 years?

He's not going to play at this level for the next 3 years. Also, the Mavs are not going to win a finals in the next 3 years, either, as they're going to have a target on their back from now on. The hardest thing to do is repeat for a title because every team in the league will take you more seriously and the team's hunger to win a championship has decreased.