I agree with most of what you wrote here but, to be fair, the Oracle is a pretty reliable source of information. If you pay her a large amount of money for a "major consultation" she will explain one of the main game mechanics in detail. If you focus on gathering a lot of money by selling things to shops, you can pay for multiple major consultations in a single game and create an extensive set of notes to work from. Here's an example of one those major consultations:
Behold the cockatrice, whose diminutive stature belies its hidden might. The
cockatrice can petrify any ordinary being it contacts--save those wise
adventurers who eat a dead lizard or blob of acid when they feel themselves
slowly turning to stone.
There are stories of purported unspoiled ascensions[0]. Whether or not you believe them is up to you. It all does seem plausible though.
The Oracle does seem to have been devised to make unspoiled ascensions possible, even describing the invocation ritual in detail. The Quest leader also tells confused players what to do after retrieving the Amulet (interestingly, with widely varying levels of specificity depending on the player's role).
Still, I've never seen any specific unspoiled ascension stories apart from Timothy Nodine's, so I wonder if that's the only one in history, or at least if it's happened fewer than half a dozen times ever.
[0] https://groups.google.com/forum/#!topic/rec.games.roguelike....