The real roadblock with Japanese, in my opinion, is how kanji makes it impossible to absorb new vocabulary through casual reading. We naturally infer the meaning of words from their syntactical and semantic context, but with kanji there's no "name" to hang the inferred meaning to as you read. You can't pronounce it in your head, or out loud.
Kanji make it possible to sometimes guess the meaning and pronunciation of a completely unfamiliar word, but even in those cases it's just a guess. You can never be certain. And in fact, since you can't be certain, it means you need an entirely separate type of dictionary to look up these words, a reverse-kanji dictionary where characters are categorized variously by the number of lines, the presence of certain components, and other schemes of native and non-native invention. This is because you don't have a name for the word you're looking at, whereas in almost every other language, the "spelling" of the word is the name.
About four years into Japanese, the same point where in my Spanish studies I was picking up Don Quixote and enjoying it, I was struggling to cope with young adult fiction. No, I was completely defeated by it. Every page was a slog and it was impossible to progress without turning it into a study session where I looked up the pronunciation of every single unfamiliar word and repeatedly practiced writing unfamiliar characters.
At some point it becomes simply impossible to progress without active, intentional study. The so-called "osmosis" hits a hard asymptote and it's because of kanji. Reading fiction for 12 year olds means pencil, paper, and two dictionaries to decipher it. Or it used to; I guess mobile apps that can OCR the text and look up words have made this process vastly easier for younger learners.
The article is paywalled so mea culpa if this point is addressed in there.