this is a beautiful post and i am reluctant to spoil it with banalities but
a few years ago, for various reasons including a medical process that left me functionally blind for a couple days a month, i started listening to audiobooks way more. i'd already listened a bit, but they became my primary means of consuming fiction, especially.
i still listen to audiobooks even though i need to less than i did then. but i have a specific way i do this: i also have the book, on page or a screen, and i go back and forth. i listen when i'm driving or taking a walk, and then i flip forward in the book when im eating or in bed. i then skip ahead in the audiobook the next time i need it, repeat.
the other day i started an audiobook of rebecca, which i've been putting off reading for some reason or another for a decade and a half. i ended up enjoying it so much that i did what i also did with udolpho and middlemarch, and just put it down halfway through and mowed through the text instead because it was faster to get through and i was hungry for it.
when i think back on these experiences of moving back and forth between the written word and the spoken one (and maybe it is because i am so choosy with my narrators?), i cannot remember, usually, which parts i read and which i listened to. the narrator's voice in my memory is influenced by my own conception of the characters' voices; my characters' voices are sometimes informed by a subtle bit of performance from the audiobook narrator giving a shade to their characterization that may not otherwise have become clear until my second or third read. these things meld together seamlessly and by and large i cannot sort them out from each other*
i don't pretend to speak for every reader or listener but my own experience as someone who turned to audiobooks first from necessity and then kept them from convenience but still reads the written word as well has led me to believe that there is maybe less of a stark difference between these things than people want there to be. i always hear the argument of "but you can be distracted if it's an audiobook!" as if i don't regularly hear readers jokingly bewailing their own tendency to read ahead of where they are because their eyes caught on an interesting sentence two paragraphs down. as if we haven't all had the experience of realizing we've read three pages and need to go back and re-digest them.
and there's something else too that the op touches on here (to finally get back to the point, sorry, lmao): a skilled performer can give you understanding that you did not have. for me, raised on old classics, it is very easy to understand the sly wit in a line from austen or the quiet despair in a particularly poignant bit of dialogue from eliot.
to someone who has little to no experience reading language from another time - which is a lot of someones - but wants to learn, and would benefit enormously from giving themselves the joy of access to all the wonderful things made when people spoke and wrote differently - to those people, now, i recommend that they open the book and turn on the audiobook and read them alongside. this is, after all, how you're supposed to learn shakespearean language, right? you listen to an actor giving life to those lines, and the language slots into place, and you realize in time you can turn to the page and what was a puzzle to you before is now very clear.
audiobooks can make people *better readers.* to someone who loved watching pride and prejudice but found themselves frustrated by trying to read northanger abbey on the page, what a joy to listen to a performer unlocking the understanding. what a joy, then, to pick up the last half of northanger abbey and find that you have, in essence, learned a dialect - even a language - that was inaccessible to you before.
anyway. as i said, my own experience leads me to believe that there is less difference between these things than people want them to be. but there IS a difference - a huge, wonderful difference - for someone who wants to learn, and i am never gonna shut down anything that makes life easier for someone who wants to learn and be able to enjoy more things in life, especially stories.
* with the exception of a VERY hilariously delivered scene in middlemarch by the inimitable juliet stevenson which is so fucking funny in her voice that it made me laugh til i was lightheaded, and which i now always read in her voice - and what a delight to have that voice in my head when i read it!