Pretty good.
The 55-38-7 numbers are not for all communication and are actually based on feelings and attitudes of like/dislike only. They are often misused to convey the importance of understanding non-verbals. Which for some of the reasons you covered, is quite important.
They do not cover written communication at all but if one is very good with syntax, it can be used party like reading non-verbals. It is easier when the person or usual writing styles are known, this is why watching their writing habits online over time can give valuable feedback.
I would use these numbers in class to encourage students to stress less over grammar and start getting interested in the full range of communication. I'd also use it as a way to demonstrate manipulation through quoting studies and statistics. It is a versatile rule.
I was half way through writing a related article when I saw this down the feed. I will post it tonight if it gets finished.
Excellent points. I am looking forward seeing your insights in detail