You question involves a misrepresentation of how science works. Science doesn't prove anything. Rather, scientists make progress by doing the following, as explained by Karl Popper (see "Realism and the Aim of Science", Chapter I). (If they don't do what I'm describing they don't make progress.) (1) They propose ideas to try to solve problems with current theories. (2) They then look for problems with their proposals, such as failing to solve the problem they were created to solve or clashing with a new experimental result. (3) Once they have a theory that solves the original problem and doesn't have any outstanding problems they start to look for problems with the new idea.
So then the question that should be asked is, if there is a superposition of states before measurement how could that idea be tested? What testable statement would have to be true if there is a superposition that would not be true if there was no superposition? There are many experiments that do such tests. If you do a single particle interference experiment in an interferometer and put a phase shifter in one arm of the interferometer that tests whether there was a superposition.