A lot of excellent observations.

But you did answer your question when you mentioned most older scripts were illiterate (in the academic sense).

Illiterate scripts inherently carry a lot of information whose priority is to convey the message independent of the listener (I’m guessing)

I think languages that can convey tone are awesome. It makes the language richer and less ambiguous

Hindi or any Indic languages (popular ones) have any case differentiation.

Mostly because emphasis on any word is not literal it is tonal.

So there are these things called - matra (12 matras in hindi)

They are symbols representing inflection/emphasis etc. and we can combine them with each character of the alphabet and convey tone.