Nit pick, but proof by contradiction is necessarily stronger as it is deductive reasoning, and this kind of "proof" by anecdotal evidence doesn't rise above abductive reasoning. Still useful, very much not a proof.

True, but in this case these are hardly globally applicable facts about LLM-based systems (not nearly to the same degree as "12 divides 2" anyway). Different systems have different properties on all those fronts.

I don't think no argument is the right substitute for a bad one!