There is two things which needed to be fixed imo.
-) When some part of ball is touching the stumps then according to DRS, its umpires call, but on certain occasions, it shouldn't have been. Because
.) When more than half of ball is clipping the stumps, it will definitely dislodge the bails. Almost equivalent to the case when total amount of ball is hitting the stumps. See the screen-shots below
The first one was given not out while second one was out, all because of umpire's call.
Practically, both don't needed umpire's call since huge amount of ball is hitting the stumps, while second one is merely clipping, highly unlikely to dislodge the bails.
The point is, that ICC should narrow the window of umpire's call. When enough amount of ball is hitting the stumps, it should be out instead of umpire's call like in the first case, while if very minute part of ball is touching the stumps, it should be not out instead of umpire's call. In both cases, the decision can be made independently without relying on umpire's call.
Umpire's call should only be used when there is enough doubt, not in cases the clear cases like above two.
-) Another thing, in case if decision stays with umpire because of umpire's call, the team which has used DRS shouldn't lose its review. They have made a fair decision of taking a review, and still being penalized twice for that. Once, by the decision not being given in their favor, secondly, by depriving them of a review.
These things should be regulated better by ICC.