Can you explain why a stream of hiragana would be unreadable? It's a phonetic alphabet, right? Shouldn't it be just as readable as the phonetic alphabet for any other language?
In this video, Yuta compares different ways of writing the same sentence and discusses efforts to eliminate Kanji: "Why Do Japanese Still Use Kanji?" • https://youtu.be/O27TgLW6pCU?t=220
Another analogy: I find the flat enunciation of "voice to text" on my phone a bit difficult to follow. I can understand if I pay attention, but I can't passively listen and multitask like I can with human read text (@see - The Guardian's "The Long Read" podcast).
As an example, my wife owns a Japanese CD which includes a couple of songs originally from my own country, but translated to Japanese. Listening to that is very easy, I hear every word.. it's much much harder to actually get the words if I listen to the original in my own language! And these are simple songs.
EditAdd: What I said above is correct in the sense that it's easy to listen to Japanese, as in actually hearing the words, but yes there are homophones which sometimes make me, a low-intermediate speaker, not understand what I hear. I hear "another" similar-sounding word, unless there's pitch to clearly identify it, and then what I hear doesn't make sense unless it's a recording and I can re-listen.