I am 100% certain that you could write something of a technical nature relating to your discipline that most of us would have difficulty following and would find poorly written. I am equally certain that I could do the same for my discipline as could probably any of the other respondents in this thread. That's what happened here. Someone wrote to professional colleagues using the technical vernacular that is used in their discipline and its meaning seems unclear to you. Different disciplines have different conventions in writing. So what? This is something my husband and I have noted when discussing or proof reading each other's technical writing.
It wasn't a piece of technical writing. It was an email to staff and students.
In a way, your sentence above, which I bolded, is the entire point of what you linked in the OP. I am also equally certain that you could write something in an Australian vernacular that we Yanks would have difficulty parsing out and would think was poorly written. I know that I could do the same for you--or even just quote some great American literature for the same. And that's the point: People from a variety of backgrounds may have different speech patterns, different uses of words or even different vocabularies that they use to express themselves---and that should not be punished by poor grades or overly correcting grammar, syntax, etc.
I have not anywhere criticised the idea or use of critical grammar. I criticised a particular paragraph that was about critical grammar as being poorly written.