The Mavs already had the best offense in the league and were playing at a 58-win pace. I don't think Rondo will improve them in either area. He could help them defensively on the perimeter and boards, both areas where they're lacking (even Rondo's declined defense is a big upgrade over Jameer Nelson). But I think the main reason they got him is the Mavs are 0-5 against teams ahead of them in the West, all of whom have elite to excellent point guards, and their offense actually sputtered in some of those games. They're hoping Rondo can give them an edge to compete against those teams specifically and obviously in the playoffs, where they were looking at a first round exit if they did nothing.