Thread by @Gregor_Wakounig

I've got some questions for non-native japanese speakers/learners (natives are welcome to contribute to this thread, too).
It's about 漢語 vocab if there is a possibility to learn it without dull rote memorisation. It's a topic I've been thinking about since years.
Thread 1/x.

First of all: I speak five languages. 2 germanic (german native, english learned), 2 slavic (slovene native, serbocroatian learned) and have some okay-ish passive command of italian/spanish.
And, of course, Japanese.

I honestly can't even remember how I really learned english and serbo-croatian. It just "kinda happened".
Well, of course I know what helped: They are similar languages, so the amount of vocab and grammar I had to learn anew was comperatively low.

Example:
The english "table". Even without ever hearing it, I instantly knew the meaning, especially when context was given: "Let's sit at the table".
There is the german word "Tafel", which today mostly means "Blackboard", but also has the archaic meaning of "table".

The same goes for slovenian and serbo-croatian.
And for romance languages? Well, there is Latin. "Politica e una cosa difficile" means "Politics is a difficult cause" or "Politik ist eine diffizile Causa" if I translate it into strange, but understandable german/english.

Result: I understand romance languages to a certain degree thanks to Latin.

But now, let's turn to Japanese.
Of course, JP is not an indo-germanic language, so there is next to zero vocab which I can infer the meaning by comparing words to another language, except katakana words

Well, that's just how it is, so if course one has to memorize a big chunk of vocab to become conversational. From this, one can infer the meaning of a lot of native japanese words without bigger problems.
Example: 読む + 終わる = 読み終わる = to finish reading.
Easy, isn't it?

Even if one would hear those native japanese words for the first time in a conversation, there would be no problem at all to know the meaning.

BUT!

Then there is what I call "Random Onyomi-Chaos".

What's that? Let's take the word 救急車. Imagine you've never heard/read this word and it suddenly comes up in a convers.
It's made up of three On'yomi, which could belong to a big number of Kanji.
So without seeing how it's written, how in the world can anyone guess the meaning?

It could be written 旧急者, 級糾社, or simply just 急救車.
If the word would instead be 急いで救う車: I would instantly know what it means.
But without looking it up, I find myself guessing Kanji "from context" far too often. Not good, when you're in the middle of a conversation

So I was wondering: Am I the only one with this problem?
I have the impression that this is never adressed from a linguistic/language-teaching perspective. How come??

Happy to hear all your thoughts.

And yes, this and exactly this is the final boss of the Japanese language for me.
Random On'yomi stacked upon each other without having a clue which Kanji they belong to.

And yes, I actually DO have a okay-ish command of 漢語. The thing is: I acquired this knowledge mostly by rote memorisation of random syllables derived from ancient chinese which belong to certain Kanji. This just feels like a very odd and unnatural way of language acquisition.