Absolutely fascinating study. I look forward to more as the density of materials rises.

I would observe that calligraphy such as in Islamic art, frequently conveys two messages. One is more abstract such as it's compelling beauty, but it can also be strongly representational. A word about swans in the shape of a Swan.

So I don't see "it's just decoration" as a strong rebuttal. It may be decorative. It can also convey meaning.