I get this point you are trying to make but I don't agree with your implication that it's a relevant issue when the Spurs have NBA proven players in Neal and Anderson ready and more than capable to fill in the void at the SG spot (where Hill played 80% of his minutes).
Spurs won't lose much if at all with Hill being gone from an offensive perspective because of Neal and Anderson deserving and worthy of more minutes and being just as good or better shooters than Hill (Hill was more of a spot up shooter than anything else). Hill was expendable, even if he was a rotation player last year.
That being said, I don't see this team taking a step back from offensive perspective with Hill being gone (Spurs have a lot of weapons outside of Neal/Anderson as well). Furthermore, the Spurs improved from a defensive perspective as they drafted the best small forward in the draft that happens to be very defensive oriented and gifted (6'7" frame- 7'3" wingspan). And at the same time, the move allows Anderson to get quality burn now-- who is a damn good defender and has to size to guard wings more effectively.
Last year, the Spurs used Neal and Hill quite often at the 2/3 spot behind the Jefferson-Ginobili-Parker starting lineup. Neal and Hill were asked and forced to guard long 2's and 3's quite often and their size was a glaring weakness from a defensive perspective (Sam Young, Vasquez, Allen had a field day in the first round). With this move, Spurs now have minutes available to integrate wings w/ size (Leonard/Anderson) into the rotation. And they still have Neal in their arsenal as well.
I don't see how this sets the Spurs back for now or for the future. If Spurs traded Hill for a questionable late first rounder ( Jimmy Butler) and didn't have quality depth at the two spot (Neal/Anderson) then I'd agree with you. But that is simply not the case. IMO