I don’t know about “market inefficiency”, simply due to the fact that NBA transactions are a zero-sum game. There is pretty close to a finite number of assets in the league (back-of-the-roster, signed-off-the-street free agents being the only real uncontrolled asset). Over time, front offices will win some and lose some, and the better front offices will win more than they lose, or get creative about using the entirety of the options available to them to win (see Morey buying the nonguaranteed contracts to include as filler).
I’d argue that the real market inefficiency for NBA teams is player development. Wouldn’t every team love to have Chip Engelland overhauling their players’ broken shot?