I'm not sure I follow. You mention why it's prudent to not disclose Trump's investigation, which I agree since what you said is the same reason why the FBI never comments on investigation.
But you also mention there's a reason to discuss re-opening the Clinton scandal but don't mention those. In fact, you say it was absolutely the wrong move, which I agree, but you left it at that.
The frivolous "scandal" bout Loretta Lynch was that, frivolous. Even if it stuck, the FBI is (supposed to be) above petty political scandals, there was no reason for Comey to react to it. The only prudent course of action is to not disclose either, because that's not what the FBI was supposed to be doing. But if he absolutely, 100% HAD TO disclose the existence of one, the ONLY way to remain bipartisan was to disclose both.
Of course, disclosing both was not an option, which further fortifies the fact that he shouldn't have said anything in the first place.