Re: if you switched garnett with dirk or duncan, woud either team improve?
I agree with some of the previously stated comments. The Mavs seem to be created around Dirk. His ability to hit a shot from almost anywhere on the court spreads the D and creates openings for penetration. You wouldn't get that with KG on the team.
To give KG some credit, he'd bring Dallas's D up.
I don't know about Duncan. He's definitley one of the best players in the league and also one of the best of all times. His footwork is beautiful to watch, but overall he's pretty damn boring to watch all the time. Now to address the question, I'd keep Duncan with the Spurs.