Very well, I'll rephrase.
Yes, it was a good blog post.
> "this is the definition of ad-hominem"
It is not. Ad hominem would be "his argument is false because he is [personal attack]". Ad-verecundium would be the specific case where the personal attack is "he's not an expert in the subject".
Cautioning against grandiose claims by pointing out the author has made unverifiable grandiose claims before, which are objectively beyond their expertise, and was unable to defend them or reason properly against a peer with known expertise, is not an ad hominem. It's just skepticism. Having said that, good for him for doing his bit and writing the blog post. I've done far less.
> also black-and-white thinking (100% right or 100% wrong):
I think you are misreading this, so I apologise. I'm not advocating "splitting". The point of the "he may be wrong or right" part is that the only way to evaluate his claims of "what a public figure should do" etc, is via the conditional fallacy, i.e. "This is the correct course of action because IF you did the opposite, THIS would have happened". This is effectively an unverifiable claim, which is why, as a form of argument, it is fallacious. His claim in absolute terms, however, may in fact be true. Or false. We can never know.
Now obviously, you might say, "but he provides evidence for his opinion on what a public person should do". True. But here is where the earlier argument comes in. It's worth keeping in mind that this is a blog post, by a non-expert, who has shown inexperience against experts previously, and where he is free to take creative liberties to promote his view, as he has done in the past. It is not a scientific article that has undergone peer review, nor is it a disinterested exploration of the literature. It's purely an opinion piece (albeit a well-meant and well-presented one) backed by the evidence and visualisations he feels make his point and linear narrative best.
Which is absolutely fine for a blogpost. Kudos to him.