I'm under the impression that the viral precursor they were expecting to find in animal populations has not been found (and that if it were a natural occurrence it would have been found) and that at least one researcher at the Wuhan lab had previously proposed gain of function research like this before. I'm sure stranger coincidences have happened but with that in mind I think its fair to elevate a lab leak theory from 'premature/purely political in intent' to 'reasonable'.