So I would say this text is biased by the "western" view of the writer, something that could be categorized as "Orientalism". A study about this phenomenon is valid, is important. But this post is not a good study.
Edit. I should have realized that. I just came back from China and my kids were watching a children's show with the following subtitles: "一二一二一二一二一二一二一二一二一二一二". Took me a while to realize the subtitles were not broken. The characters were marching chanting "one two one two..." :)
I tried the same with Google's IME and I couldn't use digits as input, like the Japanese IMEs let you do. I could find the character for 叁 quickly enough, but 壹 was only on the second or third page. Still, I suck at Chinese and I found it.
Now, writing these characters is an entirely different story. I think any character that's rarely written and appears only in one common word runs the risky of being forgotten, even if that word is quite simple and used on a day-to-day basis. A word like 喷嚏 (sneeze) in Chinese or 薔薇 (rose) in Japanese fit the bill.
The Japanese fallback, in case you forgot the character is quite simple: you'd just use either Katakana or Hiragana with different connotations[1]. I'm not quite sure what the fallback would be in Chinese, but I guess that would often be picking another character with a close or same pronunciation, as Chinese speakers often do on purpose as a sort of pun.
I also expect there are still fewer cases of "character amnesia" in China than Japan, since the fallback mechanism is simpler and more standardized in Japan, and children are taught far less Kanji in school than their counterparts in Mainland China, Hong Kong or Taiwan.
[1] While Hiragana gives a familiar connotation, writing the word as バラ in Katakana is "more official", if anything, since names of flora and fauna are conventionally written using Katakana in official contexts, especially when you want to use the exact scientific name. This is the equivalent of using Latin names in Western countries, e.g. Rosa hirtula would be サンショウバラ.
Does that work for larger numbers, keep adding strokes?
That's not to say it's never done, but it feels like an outlier. As if a friend found a word too hard to understand and drew a picture instead, and then the author wrote an article about how spelling is so difficult that it leads English speakers to draw words instead of writing them.
But the thing that struck me the most was just how confused people were when I asked them about it. It just didn't seem to be anything that was an actual issue for them.
The analogy I've used in the past is, you read kanji with your mind but you write them with your hand, so being unable to remember a kanji is more akin to forgetting a guitar chord or a keyboard shortcut - if your hands stop making the motions, you'll eventually forget them.
In my experience, most people of my generation have generally forgot and usually just write "lower case letters but big" or block letters.
So yeah, I don't think there's anything inherently chinese about forgetting writing things you don't use.
[0] https://www.genitorialmente.it/2016/10/alfabeto-corsivo-maiu...