I still think that something else was unethical: not running challenge tests.

There were enough volunteers for them.

Gamble is the wrong word for this. It was a calculated risk as is everything in a pandemic or other evolving threat to public health.

No one ever claimed that it was the best option, just that it was the only option clinically tested. It would have been irresponsible to recommend a different option without at least some limited clinical trials. Sometimes you can't wait for perfect data.