It's an interesting read. I disagree that a novel needs to have intentional subtext to be considered a novel instead of 'just' a novel length story.
A friend of mine once told me a story about a time when he was in high school. He had to do a book report, and he knew a writer lived nearby. So he went to visit this writer to talk about his novel. And one of the things my friend brought up with the writer was the subtext that he had read in the book and he asked if he was correct about seeing that in the book. The writer's response was something along the lines of "That's a really cool subtext you found in my novel. I should use that the next time someone askes after it."
I think readers tend to read a lot more in novels than is necessarily there. Yes, some writers put it in intentionally. But others just tell a good story and the readers still find subtext in there. If there were only intentional sub-texts and not also reader invented ones then there was no discussion possible about novels.
For me the difference between novels, novella's, short stories and so on is the complexity of the story. A short story focusses on a single thing (event, character, and so on). Novella's have more events and more characters. And novels are more complex still. There's no hard and fast rules, which is why there's always debate about where the boundaries lie.
Which is not to say that sub-text can't help in telling a great story. I like the reminder of using it to increase the emotional impact of the stories climax. The idea of combining the character's climax with the theme and sub-text sounds very powerful, in the same way that combining the climax of a character arc and a story arc does.
As a long time lang and lit scholar, I see great value in subtext, and my favorites are the ones I, as the author, never knew were there. We just picked up a research book the other day, https://www.amazon.com/gp/product/B07QHJP155/ , that opened us up to an entire new world of motivation and initiative for one of our main characters. It makes perfect sense, it reconn's beautifully, and he'll never be the same again!
Long story short, yeah, sometimes the curtains are just blue, but what magic does it bring to the story when they aren't?
Hmm. Now, I'm not being critical here, but... What you suggest about sub-texts etc works fine IF you don't have something like dyslexia. You would probably say that I write by the seat of my pants. That may be so, but it isn't a deliberate choice. I have enough trouble getting words down on paper without trying to outline, make notes, write down my themes and sub-texts etc. It isn't a realistic option for me. Do my books have sub-texts? Maybe. I'm told that they do. But I've never made a deliberate choice about a sub-text, it just happens. Maybe I'm lucky. But I sometimes think that we forget that our primary objective as authors is to entertain. Because if we don't then we won't sell many books. LP Hartley's The Go Between is often described as a great novel. But compared to one of Dick Francis' bestsellers? Which do the readers prefer?