Maybe you will find this interesting: graphic designers have lots of rules about the proper use of typography when laying out a document, like correct kerning, use of old-style numerals, ligatures, etc. The reason for following those rules has to do with the same principles of harmony and naturalness in this blog post, but when researchers tested the impact of "good" typography vs. "bad" typography, they found no differences in performance measures like reading comprehension or reading speed. They did find differences on other measures - in the good typography condition, participants underestimated the amount of time they had spent reading (a measure of engagement with the task) compared to participants in the "bad typography" condition.

But the most interesting finding was when they tested creative cognition - on that test, the "good typography" participants scored much better than the "bad typography" participants. This might explain why we designers insist on good typography (and other design principles). Creativity is a big part of our job, and we want to avoid things that might impair the performance of our creative cognition. But for people in other, "left-brained" professions, enhancing creativity is less important and engaging people is less important, so it makes sense that they would see design rules as irrelevant extra work of little value.

Designers rush to judgment when they see "bad" design because it almost literally hurts their brain. But, maybe the person who designed it or the audience for it doesn't have that kind of brain - and that's OK.