No novel virus has ever spilled over from a lab. Every novel virus in history has been a zoonosis.
The only lab escapes were of existing, highly infectious viruses that were being intensively studied, cultured in large quantities, etc. Such escapes are rare, and there are very good systems in place to detect them. The Wuhan Institute of Virology regularly tests its workers for antibodies against various viruses (including coronaviruses), and the workers are negative for SARS-CoV-2. The pandemic flu you're talking about was likely the result of a large-scale vaccine study, not a lab leak.
There is no sign that anyone knew of SARS-CoV-2 before the outbreak, much less that any lab was working with it. There is, on the contrary, good evidence that it was not known about. The WIV never published the genome of SARS-CoV-2 before the outbreak, in contrast to other related coronaviruses (for example RaTG13 was published in 2016, and the WIV has never even isolated it - it exists purely as RNA fragments and data on a hard drive). The set of coronaviruses that the WIV works with are publicly known, and SARS-CoV-2 is not among those worked with pre-2020.
> The ad hominem isn't really persuasive.
If a person who clearly does not know anything about programming writes a long screed about programming, filled with basic errors that illustrate that the person does not understand basic programming concepts, it's not ad hominem to point out that the person doesn't know anything about programming. The question is why the media is hyping an article by someone who doesn't understand basic virology.
> WIV removed their virus database from the web on Sept 19, 2019
This part of the conspiracy theory requires the WIV to have known about a lab leak in September 2019. That really is stretching any sort of plausibility. This database was only online for a few months in the first place, and they say that they took it down because it was insecure. The alternative explanation that the conspiracy theorists are pushing - that the WIV knew about a lab leak months before anyone in China showed any sign whatsoever of reacting to the outbreak - is just not plausible.
> their staff/student bios from the web in late Jan 2020.
I don't know what bios you're talking about. However, there was a conspiracy theory about a postdoc who left the lab in 2015, whose picture was "missing" from the website. Based on this, internet conspiracy theorists jumped to the conclusion that she was patient zero, that she had been secretly cremated, and all sorts of other nonsense. The obvious explanation is that she left the lab years ago, and that for whatever reason, nobody has bothered to put her picture up on the website.
> Access of investigators to the WIV has been blocked. Free staff interviews with foreign investogators have not been permitted.
This is false. The WHO team was given full access to the lab, and interviewed many of the staff. They got detailed information about all the coronavirus research at the lab.
> The US gain of function establishment has pre-emptively sought to associate any talk of lab leaks with social stigma and conspiracy theories.
I don't know what the "gain of function establishment" is. Virologists generally view the lab leak as extremely unlikely and completely unsupported by evidence. Some virologists do what might be characterized as "gain-of-function" research. Does that make them the "gain of function establishment"? There isn't some big conspiracy to shut down truth-tellers. There are experts who are annoyed that an extremely unlikely theory that is unsupported by any evidence is being hyped by non-experts who don't know what they're talking about.