This is an interesting take, and one I have some sympathy for – the Bible, after all, says to “study to show thyself approved.”
However, I think there’s another big question you raised – namely, about the Holy Spirit. Certainly, God made many people without the patience for, intellect to understand, and interest you have in these ancient writings. And these people, presumably, could be no less devout or beloved by God.
If, unlike esotericism, Christianity is not an elitist religion – if God, as Jesus said, really has hidden things “from the wise and prudent and revealed them unto babes,” wouldn’t it also follow that the Holy Spirit could establish a single church, a single teaching, that had the authority to dispel errors? Christ himself prays that Christians “be one.” And the Church claimed this authority for over a millennium. Eventually, tragically, there was a division among many apostolic churches, but they all hold to the same creed, and at least the council of Nicea.
And you can find tons of documents that weren’t included in the Bible. Many of the texts of the earliest Christians – and I’m not talking about Gnostics, but very orthodox Christians, saints, Church authorities, etc. – are readily available online, as you seem to be aware.
If the Holy Spirit is really omnipotent, wouldn’t it follow that He would be able to offer a reliable teaching to His children? Not something that has to be determined by each individual, but a truth that is revealed by God himself.
After all, if it’s up to us, it seems we’re doomed…