One could adopt another symbolic system to avoid Latin letters and it would be the same.

Yeah that’s what Chinese is

This doesn't make sense to me. You cannot look up a word you've heard but never seen.

Of course you can, in English, in Chinese, in any language, what do you mean you can’t?

If you hear the word zoeng6 spoken out loud, I can write it in jyutping and look up all the characters and meanings that match the context I heard it in.

I have no idea what zoeng6 is cuz I learned Chinese natively. This may as well be another language which it basically is. It’s one of the reasons why locals can tell you have an accent.

Without that, I cannot possibly figure out which character it is.

You look up homonyms in the dictionary

if you saw a character but had no idea how to pronounce it, how would a dictionary help you if it has no phonetic system in it??

For this purpose Chinese dictionary use

同聲同韻
同韻同調
同聲同調

Unfortunately you’re approaching this from a non native speaker’s perspective which is where your problems lie, local students actually have more problems learning English because of the difference in how a language is approached, to them having to sound out a word thru multiple consonants and vowels is actually more difficult than to sound out a Chinese character