Tony is a great young player, but you gotta understand that Tim Duncan is a huge reason he gets those wide open layups every two seconds. He demands doubles, and those doubles come off of Tony since his jumpshot is the most suspect of the Spurs main players.
Not to say he wouldn't still be a very good player without Tim, but we're talking about a PG here. AI is the ultimate scoring PG of this era. What has he won?
Every team goes through cycles. The Spurs are one of the rare teams that skipped a cycle because of David Robinson's injury that gave you Tim Duncan. Unless you plan on doing that again then the Spurs (and Pistons) will fall out of contention in a few years. It's inevitable. Luckily for us, our teams have good management that will turn it around before too long.