Like the title suggests, the main point of this comment is to highlight the fact that paying someone their market value does very little to give your team an edge. In fact, in a perfectly rational and accurate market, if every team paid players exactly what they were worth you would by definition end up with a team that wins 42 games and loses 42 games.
I understand the allure of a moneyball approach to roster building, but it really isn't the be-all and end-all of the sports executive's playbook.
In the scenario that you describe, there would likely be any number of different win/loss ratios for a few reasons. Firstly, if you're going to go with the numbers approach, you have to accept that basketball is a stochastic system (wins and losses are to a large extent probabilistic), so while win/loss ratios may be normally distributed with .500 as the mean, in most permutations every team will not end up at exactly .500.
More importantly though, you are ignoring the effects of gameplan, chemistry, and coaching. In this scenario, the Spurs probably still win the Championship, because their front office is going to assemble a team that makes sense, and Popovich is going to have them playing the right way. This is exactly what Danny is trying to do with Stevens and his free agent signings. Putting together a market-value team is not necessarily a ticket to failure as long as your pieces harmonize and your coach has them playing to their full potential.
I actually fully agree with what your saying. Obviously things like team chemistry, coaching, and cohesion can be complimentary to moneyball style roster-building, and one doesn't have to be done at the expense of the other.
I honestly think that a team needs both in order to win a ring, and I can't think of a single team that managed to win a championship without a stacked roster. Even the 2005 Pistons had Ben Wallace and Chauncey Billups in their primes getting paid 5 mil apiece. That's ridiculous