LLMs write samey English that is of significantly higher quality than the median literate native speaker. There's a difference between obnoxious writing and bad writing, and when you claim LLMs can "barely speak English" you've run off the rhetorical cliff of your argument.
I agree with you contra GP that "barely speak English" wildly misrepresents LLM capabilities, but I think they don't write very well, and your characterization is also an overstatement. They often use stylistic elements that don't make sense in context: pointless metaphors, abuse of bullet points and tables when a simple paragraph would do, excessive parataxis, misplaced emphasis, dense technical prose even when unnecessary, occasionally weird word choices.
Those problems are much worse in languages other than English, by the way. I'm not a native speaker but I always interact with LLMs in English because their prose in Italian is terrible, it often reads as though the text had been written in English and then translated.
Obviously there's nothing wrong with each of those stylistic elements in abstract, exactly like there's nothing wrong with em-dashes or the word "absolutely", but I would argue that writing well means choosing styles that match the content; what LLMs appear to be doing instead is forcing the message into a default pattern, which we percieve as forced and therefore tend to dislike.
To be clear: their writing is fine. The primary goal of writing is to convey meaning, and LLMs have been perfectly adequate at that pretty much from day one. I can get over their quirks.
The bar they set was "barely speaks English".
The bar I set was "significantly higher quality than the median literate native speaker".
The bar you're setting is expert use of metaphors, restrained use of bullets and tables and parataxis, proper emphasis, and avoiding dense technical prose.
I suspect you have a higher opinion of the median literate speaker than is warranted.
LLM speak is of "higher" "quality" to a superficial inspection because it uses big words in a grammatically correct way.
It is worse because it fails to communicate information well. When I say it can barely speak English, I mean that it produces sentences which are incomprehensible on the first few reads. I have never found the median literate native speaker to be so difficult to understand, partly because they use a limited vocabulary and avoid waffle.
It can barely speak English in a new and exciting way, one unlike all the previous humans who could barely speak English.
I don't think the claim will bear out that LLM-generated text fares more poorly on comprehensibility tests than those of the median literate speaker. I understand the aesthetic arguments against it, and largely agree, but the technical argument you're making here is almost certainly and starkly false.
Most people write quite badly!
I would describe PIAAC literacy levels 1 and 2 as barely able to comprehend English, and someone who wrote at a corresponding level as barely able to write. They're close to the line of illiteracy, particularly PIAAC 1.
I believe the median person who comprehends English to PIAAC level 3 literacy or above, and writes accordingly, would be more comprehensible than an LLM, if we controlled for correctness and for their own understanding of the subject matter.
I think what the parent poster is getting at is that "LLMs don't sound natural". People don't write the same way an LLM does, which leads to a kind of 'uncanny valley' effect when reading AI text.
Over time, I suspect both human and AI writing will 'converge'. Humans are good at adopting/imitating language from a variety of sources, so I won't be surprised when we start using "load-bearing" in conversation. Simultaneously, LLMs will start sounding more natural.
That's in fact not what they said, though.