Alternate take: The staggering percentage of unsubstantiated reports means the IG process works.
A little perspective here... it's important to distinguish between IG investigations for alleged misconduct vs. all the garden variety IG reports that commands handle. I've received IG reports about where Gov't vehicles should park, and that there's inadequate ventilation in the swimming pool locker room. For most of these, all the ISIC IG expects is a "got it, we'll look into it" from the command. We even got an IG report from what turned out to be someone's ex-wife that claimed (among other things) that this person was cheating on their online college course. Really bizarre stuff.
Some people are very passionate about when a particular gate is open, or what the speed limit should be, or when we open certain areas for fishing. That said, even though these people should really learn to use the CO's suggestion box, very few of these kinds of complaints result in anything other than a "noted."