I understand your point. Certainly I am only Christian b/c my family was Christian in a country and larger culture dominated by Christianity. All I believe is that Christianity works for me. I am not as familiar with Ehrman as with other writers. I see a much wider range of options. Also, I am struck when early Christian fathers at how portions of scripture in differing geographic locales agree with each other. I'd prefer the precanonization scriptures. The Gnostics and other heretical scriptures were lost for many centuries. Even when I read Gnostic texts, though, they reference a story or saying of Jesus that is so familiar. It exists in western orthodoxy. The interpretation of the saying will be different but the saying will be the same.
Homer's Iliad and Odyssey were part of an oral tradition long before they were committed to text. Oral tradition was much stronger when people had few texts. Augustine had few texts compared to modern writers. Anthropologists studying such cultures report that there is little variance in the story over centuries.
Ultimately, I do not know. Pagels kept telling us that the Holy Spirit was not responsible for canon selection. Something I accepted at the time. Social and political forces were at work. We received a form of Christianity was served as politcal fusion and could be passed down generation after genernations through large masses of people. Gnosticism attracted the elite. Mysticism was exciting but like the 60s communes was not sustainable generation after generation.
It doesn't bother me that the Bible may have mistakes in it or that the authors had different agendas. Culture flows that way. Personally, I find the basics of Christianity or C.S. Lewis Mere Christianity more vibrant and so much more likely to have happened in real life. My Witness self would be appalled and horrified by New Testament scholarship. Shades of grey are possible.