The vocabulary does not seem extraordinary to me. The only oddball words are actually neologisms of Illich’s (e.g. “pleonexia”) which are quoted and explained.
I doubt someone like, say, Orwell, who complained about the stultifying use of language, would have any objection to this essay.
Pleonexia might be used in some certain way by Illich, but it's not his neologism. Or particularly new either. It's an ancient Greek word meaning greed or literally "apetite for (ever) more", where pleon = more, coming from PIE root for the same meaning.
Average reading level consensus from https://readabilityformulas.com/readability-scoring-system.p... is "college graduate". Most people read well below their theoretical grade level. For example about half of high school graduates read at a grade 8 level or below.
There have been a number of surveys of adult proficiency in reading. For instance the 2013 PIAAC. From that, I would estimate less than 2% of people can read this.
If you're in that number, great! So am I. But the complexity of the language still limits the potential audience.
to me it's always seemed like a smooth gradient, so people have a comfort level mainly reflecting the amount of effort they're willing to put in. in that case, writing in the complex style is really selecting for audience effort. this might be desirable, and might even be efficient.
I usually avoid that style, but mainly because it feels so performative.
Not so much the vocabulary but the excessive use of adjectives and the overall verbosity. It took ten paragraphs for me to understand anything new about who this guy was and what his worldview was.
I doubt someone like, say, Orwell, who complained about the stultifying use of language, would have any objection to this essay.