The core argument of your Reddit post addressing gain-of-function research is that GoF research causes the sugars on the surface of the virus to be lost.
But that doesn't address the recombination event / recombinant virus, which is what the proponents of the lab-leak hypothesis seem to be arguing (spike protein from one virus combined with backbone from another virus)
The core argument is actually one of occam's razor. Is such a recombinant /technically/ possible? Yes.
How many new assumptions does it require? A lot. Lots of people who help cover it up, lots of people who get sick and say nothing, lots of samples destroyed. And then also the epidemiological and genetic evidence doesn't support it.
How many new assumptions do you need for the zoonosis theory? Very few. It consists almost entirely of phenomena we know occur in nature, via mechanisms already described and known to occur at a frequent enough time scale to make it not just plausible, but probable.
Also, I just want to reiterate here, we virologists have literally been saying this is going to happen from nature FOR YEARS.
People like Michael Osterholm and Peter Daszak and Vincent Muenster and Ralph Baric and Shi Zhengli have been saying this was going to happen /for years/. It was a matter of "when" not "if" to us virologists. We absolutely saw the writing on the wall and saw specifically SARS-1 and MERS and knew that meant there were likely other coronaviruses that could emerge.
But funding was always so low, because the viruses weren't currently infecting anybody! So the sampling efforts were always very minimal and underfunded!
And now, because of the lab leak theory, that has actually gotten worse, not better!
https://pubmed.ncbi.nlm.nih.gov/16940861/ (this one says wet markets, which probably are an issue, but not as big as initially thought, and probably not the origin of CoV-2)
But that doesn't address the recombination event / recombinant virus, which is what the proponents of the lab-leak hypothesis seem to be arguing (spike protein from one virus combined with backbone from another virus)