An alternative hypothesis does not rule out the other possibilities, even if it provides a better explanation. What matters is what actually happened, not what provides the neatest explanation.
>>cicero+(OP)
The claim is being made that no other alternative hypothesis exists which can explain the features of the virus, so it must have come from a BSL lab.
This is an alternative hypothesis which is simpler and less convoluted and does, in fact, completely undermine the "it can't be anything other than bioweapons research" argument.
You're aiming your criticism at the wrong end of the argument.