I definitely have both inner speech and inner voice in the ways you're using them, but when I write I don't verbalize things and then write down what I verbaliz

I definitely have both inner speech and inner voice in the ways you're using them, but when I write I don't verbalize things and then write down what I verbalize. Consider that you've created an infinite regress problem. One might just as well as how inner speech is possible without preceding inner speech - clearly it must be possible for speech, whether inner, outer, oral or written to be formed from a non-verbal antecedent some way or other. If you accept that, then there's no particular reason to think that it must be inherently necessary for writing to have a verbal antecedent rather than "hooking right into" the same non-verbal antecedent.