Bray made a mistake, but not the mistake you accuse him of (for example, Evans' projected WS/minute according to Basketball Reference is nearly 3 times Burks's WS/minute -- yet Bray shows them both at 2.2). He understood how to correctly factor in minutes played. He seems to have done everything correctly, except all the final calculations are low by 22% (all his numbers are 78% what they should be if he had calculated correctly -- I have no idea how he made this mistake). If he had calculated correctly, he would have had the Jazz at 36 wins.
You are correct basically in how you attempt to correct Bray, except you have misinterpreted Bray's numbers (as far as I can tell). The numbers he gives (for example, Alec Burks: 2.2) is not WS/36, but the total winshares the players will be responsible for at the end of the year. (In fact, both you and Bray misinterpret the Basketball Reference data. It's not WS/36, it's WS/48.)
Anyway, according to this "semi-scientific" approach (which is interesting in a certain way, but I think does have problems: for example the BR projections are too dependent on career average rather than career arc), the Jazz should win 36 games.
The bigger issue, if these predictions were to somehow come true is that our presumed bench has a higher WS/48 average than our presumed starters. In fact, our bench, if the basketball reference forecast is correct, will probably be one of the best in the league, as the average of its 7 players that go into the calculation is of almost exactly average NBA players (.096; average =.100). Our starters, on average, compute to a bit below average NBA players (.086).