Yes, your belief on this is as good as mine but your comment to me about the Last Supper infers that I was flat wrong when you don't know that I was. I could just as well be right and you are wrong about this. A simple questioning without the smug assumptions attached would have been better received.
Protestant churches have also served plain, unfermented grape juice for a very long time; it 'proves' nothing except that reasonable people can disagree on matters that have little effect on anyone's salvation or worship and where the truth may only be guessed at.
I suggest we simply leave at that.