How do "poorly monitored infections of the immunocompromised" explain weirdnesses 2 and 4? (Referring to the blog post under discussion)
Did the blog author "posit nefarious secret labs"? Not that I'm seeing. There are labs all over the world doing things with SARS-CoV-2, probably for what they believe to be legitimate reasons. "Nefariousness" and "secrecy" is not in the article. "Nefariousness" and "secrecy" are not part of the hypothesis.
"a significant fraction of whom are immunocompromised and chronically infected in minimally monitored areas": Contrary to people's seeming stereotypes about "Africa," South Africa monitors SARS-CoV-2 really well. The hypothetical immunocompromised person in Alina's discussion would not be someone untreated in some remote village, unnoticed for a year and a half. No, to get that level of immune evasion, Alina must be talking about someone who was being treated medically, with fancy treatments, and being monitored for a very long time.
Well, for one thing: My first question is "Who is it? Who is this person who received all the convalescent plasma and all the different monoclonal antibodies for a year and half, in well-monitored South Africa?"
But even if we don't know who this hypothetical person is, there are other problems:
That person apparently never infected anyone else. And...that person in a year and a half never had any _intermediate_ viruses that infected anyone else either, to account for the gaps in the phylogenetic tree. And...that person had a set of mutations that you might expect to see in a humanized mouse (Weirdness 4).
You see, then, that while this is all "possible" it's not very parsimonious. I think we do better to begin with parsimonious hypotheses and try to test those and rule those out.
The lab leak is a parsimonious hypothesis -- but instead, mainstream people, for whatever reason, are portraying it as so far-fetched as not to merit consideration -- they would dismiss it, rather unscientifically, as if the hypothesis were really wild and not meriting consideration, like "Space aliens from planet X did it." Then, instead, they put forward hypotheses that are in fact way more far-fetched because they don't account for the data neatly, like "it was an immune compromised person" -- but the set of circumstances in which that would be true, while kinda-sorta possible, is much more unlikely than the circumstances of "lab leak."
The failure of the scientific community to address this really makes no sense to me.
The only question is why we didn't observe some steps on the way. And as you say, poorly monitored infections of the immunocompromised can easily explain this. It hardly seems necessary to posit nefarious secret labs when COVID is constantly spreading among billions of people, a significant fraction of whom are immunocompromised and chronically infected in minimally monitored areas.