You do realize DWS is a camunalitve stat, right? Stauskas has played 5800 minutes while Curry has played 2800 minutes... so Curry definitely has the edge in regard to DWS... Based on my adjustments for minutes played (WS ÷ Min Played x 10,000), Curry has 7.5, while Nik has 4.3.
As far as "DBPM" being in the negatives - I'm not saying Curry's a good defender, I'm just saying he's not as bad as Stauskas, and Curry's career DBPM (-0.9) is better than Nik's (-1.5).
But the reflective objective of defensive box plus minus is skewed more by random variation than offensive box plus minus is, so that's where the eye test comes in handy. Curry is much better at staying in front of his defender and not gett8ng out of position, and is a much better defender off the ball when it comes to stunting, helping, and simply keeping track of his man.