alt Hacker NewsLinguistics are orthogonal to petagogy. Something can be sound linguistically but still an in optimal way to teach the same thing. If linguistics were all there was to language learning, we would all just get a grammar reference book and call it a day, but we all know that is a terrible way to learn a language.
Personally, as a beginner/early intermediate learner, what I have found works is just to allow my brain to learn this over time by reading and understanding more an more sentences. I used Genki and am aware that it thought this badly. But it was in the 3rd chapter and by the time I reached the 6th chapter I had gotten an intuitive idea anyway (とている just sounded wrong and I couldn't explain why). And I wasn't doing much output anyway so it didn't matter that I maybe confused a couple of verb endings as I recited the 2nd writing exercise og the 5th chapter of my textbook.
"Headcanon" implies I made it up and it's plain incorrect. Now we seem to be litigating that it's correct within its scope but the pedagogical approach is unsound?
I'm not saying that I wrote this article for everyone. I wrote it for me and people like me. Specifically, for people who appreciate the rigorous-and-ridiculous — like teaching from the linguistical perspective while using romaji.
It's the same approach that my "Just JavaScript" course uses — it's 100% by the spec, but I'm using unconventional metaphors (like "wires" for variables instead of "boxes"). I take pride in making rigorous explanations approachable by slicing the explanation differently.
This is not for everyone. But it's also not a reason to say this shouldn't be written.