It isn't "whataboutism". Nobody is arguing that Powell should be treated with the same venom and bile as Clinton.
What it does demonstrate is a clear hypocrisy in those who see Clinton's behaviour as criminal and whatnot, and who were and remain completely silent regarding Powell's, when his behaviour was pretty significantly "worse" in the respects that they're talking about with Clinton. It makes it clear that those particular issues are not the source of their antagonism and bile towards Clinton, but merely the wedge they are trying to use to engage in entirely partisan attacks, partisan attacks they'd have no use in engaging with against Powell, as he's in their party.
That's not "whataboutism". That's demonstration clear and obvious hypocrisy, and that those attacking Clinton over her e-mail, or Benghazi, aren't actually concerned centrally about those events on their own merits, but only because Clinton can be slandered through them.
If we want to talk about whether Clinton "did anything wrong" in either Benghazi or her e-mail, well, we have a ton of investigations in Benghazi that found nothing to direct at her, and with her e-mail, the investigation also turned up nothing actionable.Apparent hypocrisy doesn't actually make you wrong, that's just an informal reworking of the ad hominem fallacy. Even if 10 other Secretaries of State did what Powell and Hillary did and only Hillary was getting the inspection... it still holds water.
So if you're concerned with the facts of these issues, those settle them. She didn't do anything really wrong, certainly nothing actionable, and the matters are over. And yet, they keep getting dragged up, so yes, we're going to talk about the motives of those who do so. Because the circumstances of both issues are settled, and there's nothing appreciable there.