Most people have no idea what constitutes "scientific proof," or if that phrase even has any meaning (hint: it doesn't).
More importantly, any "scientific" studies around this have a fundamental flaw. All the double-blind listening tests are immaterial to me as the finished product (a sound) is only the last piece of a process that involves a series of transactions between human and instrument. And those transactions are not blind, and hence bias cannot be eliminated. So it really doesn't matter what the "studies" say - making music is a human endeavor with quirky human issues that cannot be removed. If one's goal is to argue theoretical constructs on the interwebs then by all means quote some likely flawed set of experiments done by at undergrad at a small college as "proof." Or, you can do your own experiments and see what works in your hands and in your situations.
Having owned and gigged two basses that were identical other than wood (same construction, same electronics, same hardware - only difference were body woods and fretboard), I can say that they played and sounded different. Some might not be able to tell the difference of the sound in a mix, but I could tell when I was playing it in the moment, and that's more important to me, because how the instrument responds to me (and vice versa) has a lot of influence on the performance, and hence the final product. And that is something you can't calculate...