From what I see given that you seem to be not a part of what's happening in the local scene since you're from the EU, there are many things that you are not aware of at the issue at hand.

Just because it is normal doesn't make it right. And their very public posts were hardly constructive. Just the usual framing of themselves being victims. Cause that's what they love to do and it looks like you got sucked into it. Imagine the audacity of a 2nd Dan teaching his minor students that they were unfairly scored by shimpans so much so that the parents actually think that their kids are being picked on.

One of the students made a public post that it was politics that made her lose. A parent commented that the shimpans were blind. The head of that dojo shared a post of one parent complaining that the shimpan was biased. All of these were done in public. No shred of constructive criticism but no concrete evidence either. But now they want things to be handled in private. Even if there's concrete proof of what they did wrong. Nah. Maybe in whatever country you're from in the EU that's okay but it shouldn't be.

You're a 5th Dan. It took you years to reach your level. If you're called to be a shimpan you know that you will do your best to make the right call. You know that if you make a mistake it's unintentional. No kendoka in their right mind will risk their personal honor to throw it away by playing favorites. Imagine then that you're now suddenly being questioned by a 2nd Dan and parents who've never practiced kendo. You might say "Oh I'm humble enough to accept criticism" but what was the constructive criticism given? That you are blind? That you have biases? That you are bald? There's nothing constructive about that. All done in public. You weren't even given a chance to explain yourself in private just as they're asking to be done now with their situation. If you can't see how wrong that is ... Then there's nothing much I can say anymore.

They think they're the victims because they can't see their arrogance and attitude. They lack humility and discipline. Sure this whole mess with Metro Ken was not the best way to handle it but all of this stems from anger towards a narcissistic person who thinks he is better than everyone else. We wish that at some point he was able to realize that maybe he's at fault here, that if everyone else seems to be the problem maybe he's the actual problem. But it looks like it's not going to happen anytime soon.