Languages with very simple sentence structure are, for the most part, oral
languages. It’s the languages that have a culture of writing, developed over a
long span of time, that display a fondness for stacking clauses onto one
another to create towering sentences.

Chinese, the language with the oldest extant tradition of writing, does not have a fondness for towering sentences. For example, it forbids nesting other clauses into relative clauses. The number of characters, that means, words or half-words, that Chinese speakers prefer in a sentence on aesthetic grounds is four.

Many of the world’s oral languages are quite unlike European languages.

Whatever "European languages" means. English sentence structures do not easily translate into Finnish or Basque. But this minor nitpick is really a distraction from the infinite multitude of bad takes in this article.

Their [Barbarian language's] sentences contain few words. They rarely combine
more than one clause. [...] An English speaker might say: Would you teach me to
make bread? But a Mohawk speaker would break this down into several short
sentences, saying something like this: It will be possible? You will teach me.
I will make bread. In English, you might say: He came near boys who were
throwing spears at something. A Kathlamet approximation would go like this: He
came near those boys. They were throwing spears at something then.

Well, yes. And you will be able to find any number of sentences in other languages that become awkward when translated into English, because - gasp! - not all languages share the same set of grammatical features, nor the same aesthetic sense.

In current English, writing uses more varied vocabulary than conversational
speech, and it uses rarer and longer words much more often.

Really? When writing, where the author has time to deliberate, they're able to produce more intricately (and, thus, by Western standards, aesthetically) nested sentences than when under the pressure of speaking? This is beyond surprising!

Linguists take great pains to point out that languages with simple sentences
erupt with complexity elsewhere: They typically pack many particles of meaning
into a single word. For example, the Mohawk word sahonwanhotónkwahse conveys as
much meaning as the English sentence "She opened the door for him again."

Linguists take great pains to point out that the distinction between what counts as a "single word" and what counts as a "sentence" is entirely arbitrary. German speakers write "Eiscreme", English speakers write "ice cream" - this is entirely within the completely arbitrary realm of orthography. But of course, if you're out to "prove" that racially inferior languages don't have subordinate clauses, it's extremely convenient to just declare them a "pack [of] many particles of meaning" when they show up where you don't want them.

Linguist John McWhorter offers an astounding example from the Siberian tongue
Ket, a language in which verbs take pronoun prefixes to mark who is performing
an action. There are two different sets of prefixes that attach to different
verbs, and you simply have to know which verb takes which set. Moreover, many
verbs simultaneously take two pronoun prefixes that mean the same thing (but
many don’t—you just have to know), which trigger subtle shifts in meaning.
For instance, digdabatsaq means “I go to the river and come back a bit later,”
but digdaddaq (which involves the double use of the same pronoun prefix d)
means “I go to the river and stay for a season.” The same word with just one
pronoun—digdaksak—means “I go to the river and stay some days or weeks.”

Astounding news, folks - languages have syntax and semantics! It's also crazy how in such inferior languages, a simple sound change of a SINGLE LETTER (!!!) subtly changes the meaning! In English, this could never happen - for example, there's no difference in meaning between "I go to the river for a bit" and "I go to the river for a shit".

If such a language seems unlearnable, well, that is exactly the argument that
linguists such as McWhorter have been making: that an adult venturing into Ket
would inevitably mangle it, just as an adult learner of English may never quite
grasp its irregular verbs or idiosyncratic prepositions (why do you say in a
club but on a team?). The unpredictable aspects of language, the things you just
have to know, may be especially slippery for the adult mind—and there are so
many more of these in Ket than in English.

Guh! They almost had an epiphany here, and then they fumbled it on the finish line.