Maybe you need to learn what a proof is. A proof is something which cannot logically be denied.
Everyone logic might be different. I would assume if the Torah giving to klal Yisroel were a mere legend it wouldn’t happen to 600,000 Jews rather the Torah would be given privately to Moshe Rabbeinu and he would pass it further.
Legends can be accepted as factual occurances if not more than a couple people claim that they saw what happened with their own eyes and people believe them.
You will never find a legend that 600,000 people witnessed at once. Such a legend can’t take flight.