The more I read about the Homeric poems the less confidence I have that anyone knows with any degree of assurance, or that anyone will be ever able to know, how, when, why, through whose agency or in what form they originated or circulated before the third century or so. So much has been written about this; yet there is still no consensus, and the various views are still wildly divergent. The only evidence we have is early papyri and quotations. As far as I can tell, those don't necessarily confirm that the poems were circulating "in the form we have them" before about the middle of the second century.The gap between the preserved text and the speech as actually delivered is a interesting question. Isn't it similar in many respects to the question of how the Homeric epics were written down? (Personally, I don't believe that the Homeric epics are somehow magically different from all the other ancient texts, just because they were "oral". As if everything weren't more or less "oral" back then... The big difference, as far I see, is that the Homeric epics are much longer than any speech; I don't think they existed in the form we have them before someone wrote them down. What is left to us is not "performance", even if it originally stems from a performative tradition.)
But what's so troubling about that? Why not just accept that we have a version of the poems that has to some degree or other been shaped by Alexandrian scholars--a version in which more than two millenia of readers, Greek, Roman and barbarian, have known them--and that the evidence just isn't sufficient to allow us to draw firm conclusions about the form in which the texts existed, or how they circulated, before then? The poems are no less miraculous regardless of how they reached the form in which we have them.
Embracing the uncertainty after so many years of anxiety has made my life much happier, and I promise it will do the same for you, too!