> You can't just use China's writing system and try to make it fit to your language

And yet we took the roman alphabet and adopted it to english just fine, why was that okay but adopting the chinese writing system into Japanese wasn't?

> you can argue that they're not really literate, they just limit themselves to using a small portion of their 'kanji' and write little hiragana hints that tell you how to pronounce the written symbols for all the rest.

You can argue english speakers aren't really literate, they just limit themselves to a subset of english vocabulary, and memorize word pronunciations to understand when "ea" is pronounced like "e" as in "sear", or "air" like in "wear".

Like, I do not get at all what you're arguing here. In every language people only know a subset of the total vocabulary, and people general limit themselves to the subset that's actually used. In phonetic languages, sure you can pronounce an unknown word, but that doesn't mean you have any clue what it means. In non-phonetic languages, like English and Japanese, you may not even be able to pronounce an unknown word. In hieroglyphic languages, like Japanese and Chinese, you may be able to derive the meaning and pronunciation of a new word just from looking at the component characters and knowing their individual reading and meanings, often with better success than trying to guess an unfamiliar english word from its roots.

Modern Japanese is half Chinese in its vocabulary, hence its only consequential for the writing system to be as well. The former wouldn't work without the latter.