Gain of function is remotely possible
Something other than gain of function is remotely possible. Something other than gain of function involves a lot of improbable coincidences. Gain of function explains pretty much everything without relying on improbable coincidences.
There's a disturbing article on the lines of circumstantial evidence that point back to the Wuhan lab here:
https://thebulletin.org/2021/05/the-origin-of-covid-did-people-or-nature-open-pandoras-box-at-wuhan/
but I think Beijing would have reacted faster if it was--somebody would have realized what was going on and said something. When your run-of-the-mill doctor says SARS is back it looks like somebody being stupid. When a top virologist (Wuhan is a level 4 lab--their top people will be there) says "watch out!" it's quite another matter.
"Wuhan is a level 4 lab" is a misleading way to put it. Wuhan
has a level 4 lab. The Wuhan Institute of Virology has a lot of labs. Research on SARS was conducted in level 3 labs. Research on relatives of SARS was conducted in level 2 labs.
"The real problem, however, was not the unsafe state of the Wuhan BSL4 lab but the fact that virologists worldwide don’t like working in BSL4 conditions. You have to wear a space suit, do operations in closed cabinets, and accept that everything will take twice as long. So the rules assigning each kind of virus to a given safety level were laxer than some might think was prudent.
Before 2020, the rules followed by virologists in China and elsewhere required that experiments with the SARS1 and MERS viruses be conducted in BSL3 conditions. But all other bat coronaviruses could be studied in BSL2, the next level down. BSL2 requires taking fairly minimal safety precautions, such as wearing lab coats and gloves, not sucking up liquids in a pipette, and putting up biohazard warning signs. Yet a gain-of-function experiment conducted in BSL2 might produce an agent more infectious than either SARS1 or MERS. And if it did, then lab workers would stand a high chance of infection, especially if unvaccinated.
Much of Shi’s work on gain-of-function in coronaviruses was performed at the BSL2 safety level, as is stated in her publications and other documents. She has said in an interview with Science magazine that “[t]he coronavirus research in our laboratory is conducted in BSL-2 or BSL-3 laboratories.”
“It is clear that some or all of this work was being performed using a biosafety standard — biosafety level 2, the biosafety level of a standard US dentist’s office — that would pose an unacceptably high risk of infection of laboratory staff upon contact with a virus having the transmission properties of SARS-CoV-2,” Ebright says."