I don't think Tommy was talking about Kelly vs. Dirk in an historical sense. I think he was saying "look - Kelly should be trying to be Dirk, every day of his life, for the rest of his career."
Further, he said it's his ceiling. Ceilings, by definition are very high targets and almost impossible to reach. Tommy does not think that Kelly will be that good. But he is saying if Kelly is going to be good...then he should shoot for that ceiling.
Me - I think Kelly might be more like Sam Perkins. Which is NOT a bad result.