If you asked "Why is it that there is not one single piece of real tangible evidence that art exists?" what are people supposed to say? If I say "What about Michelangelo's 'David'?" you can just say "Michelangelo was a hack. That's not real art." and repeat the process with each new example. Because art and science aren't the same as one another and don't work the same way. Trying to come up with an example of art/theology that pleases you personally doesn't seem like a good use of anybody's time.

Besides, there are plenty of not-tangible, not-visible things we know to exist. I am not nearly as smart as this guy. But I know that even if you couldn't touch or see the plague before van Leeuwenhoek, you still died if you caught it.