It's more than that-- many people are spending a lot of time just testing FSD, filming it, actively looking for failure modes, and being quite methodical about it. We don't have the same data Tesla has about its fleet obviously, but we can all go and observe the progress being made.
Hundreds of thousands of hours of people physically demonstrating FSD technology in the real world, with production cars and real users (who are not employed by the manufacturer) is meaningful evidence, even if it happens to be published on YouTube
What a sad world we live in.