Is the wording of Google's QC Supremacy valid?
You should read the new post by Aaronson, but until then the short answers:


No.
If you can realize it in a real world machine, then it would (if no one finds a fast, classical algorithm until then).
You don't prove anything. It's a practical fact, like AI playing chess better than humans. If a chess genius is born, (s)he might win back the crown for humanity!