Good point, but I think the problem is almost always with the parsing of the advice. Receiver's perception and experience uniquely determines the degree of deviation in the interpretation. For eg. "Write short sentences" can be easily perceived as a dichotomy between fixed length vs variable length sentence, especially if you do not see the two categories, long and short, separately. Adding rhythm is merely a byproduct of noticing the recurring pattern and adjusting one's sentences. This is to say that the argument you make towards "short sentences" can also made towards your argument of writing "easy sentences".
I actually find this piece hard to read. Sitting here tired. Late at night. It almost feels like the author is writing long sentences on purpose.
I only got a couple paragraphs in. But, again, I'm tired.