Make no mistake, I like Mills, and he's playing great. But he's a shooting guard. He doesn't really penetrate, at least not enough to do what the team needs to do. They've been getting by with good shooting. But what happens when Mills comes back down to earth and he's still taking 20+ shots?
And another thing, Tony is untradeable. If crazy people think Manu is untradeable only because fans love him, then Tony is double that because the Spurs are in the lottery without him.