I'd gladly take what OKC had last season over what I'm seeing this season. Sure, it still might not end up in a title, but it ends up in a legitimate shot at one. Right now, we have no shot at a title playing bottom 10 defense. None. However, if you fill a hole by trading Waiters and the defense makes an improvement from that trade, then our chances at a title go up. Maybe we still don't win a title because maybe we now lack bench scoring, but our odds will be better and we will have an easier hole to fill in the off-season.
So, to answer your question directly, we should give up bench scoring in order to upgrade the defense. Improving the defense will do more good than losing some bench scoring will do harm.