Yeah, it's complicated so I'll try to clarify. First of all, my compliment to "authentic Christians" is backhanded. I don't think Christianity has any unique or ultimate handle on truth. It's a question of some forms of Christianity being less reprehensible or preposterous than others.

As to what the worthy insights might be, I'd go from Gnosticism to existentialism, as Hans Jonas (a student of Heidegger) did. (Rudolph Bultmann made a similar point about the four gospels.) Gnosticism may represent the earliest esoteric side of Christianity, as indicated by the Gospel of Thomas, by Paul's proto-Gnostic epistles, and by Mark's distinction between inner and outer truth (the parables being only allegorical disguises). Second, Eastern Christianity isn't as literalistic as the Western kind, and the Eastern Church is closer to the early Church Fathers.

Now, if we go with the likes of Robert Eisenman, the authentic, historical Jesus was indeed a rebellious Jew, in which case authentic Christianity would be a wildly obsolete form of Judaism (since the Roman Empire against which the historical Jesus was railing is no more; plus, the prophesied end of the world never came).

I've argued there's a good chance there was no historical Jesus (links below). If there was such a figure, we know precious little about him. Either way, because of how quickly Jesus was mythologized, the question of Christian authenticity is divorced from the purely historical question of who actually said or did what in the early first century.

We're talking about the body of work produced by the earliest Christians, not about the lost teachings and deeds of the possible founder. And it's in that body of work, including the New Testament, the Nag Hammadi library, the Church Fathers' use of allegory, and so on that we have the makings of the esoteric-exoteric distinction for Christianity. There's the literalistic interpretation of the Jesus figure, and there's the metaphorical one. The Gnostics and the Eastern Church, for example, said we each have the potential to be Christ-like. We can each be reborn, which is to say our consciousness can be broadened as we reckon with unsettling, existential truths.

So the question is whether there's wisdom to be found in Christian theology as a metaphor. There likely is, as I suggested, but that's not to say I'm a follower of Christianity in any sense.

Again, in any large organization that addresses philosophical questions, some of the output is bound to be more impressive than the rest, as far as enlightened individuals are concerned. The early Christians (Jewish heretics) had an opportunity to ponder the human existential predicament, as Rome destroyed the Jewish Temple and forced Jews to rethink their position in life. The Gnostics took that opportunity to pursue their theodicies, and their speculations are close to existentialism, as Hans Jonas showed. It's secular existentialism that I think is at the root of some of the most worthy answers to philosophical questions.

This touches also on the perennial wisdom in religious traditions, a commonality based on the possibility that theology and mysticism have always really been about our attempts to know ourselves, and we're all fundamentally (i.e. transcendentally neurologically, and behaviorally) similar. The Eastern religions are clearer about that upshot, because the Western, monotheistic religions are more literalistic or less philosophically mature.