I didn't say "primarily." I said "a lot" but I didn't necessarily mean to imply "most."
Haha, well, I apologize if I misrepresented your point, but I feel like saying "a lot" is kind of misleading, especially without any mention that there are also "a lot" of expressions that are actually quite commonly used by native speakers (even if they may seem obscure to intermediate/advanced learners who don't get daily exposure to the language).
I mean, I'm familiar with the type of arguments and analysis made on the page you linked, and while I'll grant that there is
some truth to them, I always feel the need to play devil's advocate. The language tested on JLPT N1 is not (at least, not for the most part) some kind of arcane "JLPT Japanese" that is entirely divorced from the real language. While having N1 is by no means proof of fluency (it couldn't be, since the JLPT doesn't test production), I think anyone with a legitimately advanced level of proficiency should be able to pass the test, and would argue that for those who can't, it's not because the test isn't actually testing their Japanese skill but because their Japanese skill isn't quite as advanced as they self-assess it to be. (Not trying to be cruel or judgmental about this, of course.)
I passed N1 (actually, it was the old 1-kyu before the restructuring because I'm an old geezer
) after about six years of study and three-ish years of living in Japan, and I did very little dedicated "test prep" of the type mentioned on that page. I was, however, reading extensively in Japanese and working in an almost monolingual Japanese environment, and I felt that this helped me greatly. I'll also say that even after passing N1 I still felt like my Japanese was woefully inadequate, and continued to feel that way for several years after. So I'm always surprised when I hear people say things like "I feel pretty confident about my Japanese level, but I just can't seem to pass N1 (or even N2)", because I feel like passing the test is a much lower bar than achieving the level of proficiency needed to truly function at a high level in a Japanese language environment.