The oral tradition is what gets yoked over with Plato's ontology. Philosophy isn't really native to the Greeks. They were taught meditation techniques from Eastern shaman, by The Hyperboreans...

The book takes as its starting point the enigmatic accounts of Pythagoras’ encounter with Abaris the Hyperborean.

https://peterkingsley.org/wp-content/uploads/RuizStory.pdf

Heidegger is pointing to the oral tradition with the presocratics. Its sourced from before the settled communities in mesopotamia with early human nomadic tribes.

So there's two things going on here. First there's the shamanic teachings, which actually do have a basis in "cave meditations" (or sustained meditation in temples, forests, deserts, mountain tops) and there's the cause of the ontological shift, and that's a technological problem, namely the implementation of the Ionic alphabet, with standardised vowels.

Examples of cave meditations -

https://www.youtube.com/watch?v=jFon_JXgxF8

https://www.youtube.com/watch?v=6Qtwq9C28uo

Robert Peng talks about the 100 day fasted meditation he did in a Buddhist temple in this talk -

https://www.youtube.com/watch?v=sXftbnb2vX0

Here's something on the effect vowels had on human consciousness -

https://www.tandfonline.com/doi/abs/10.1080/02604020210401

The thing about literacy is it privileges the left brain and vision above the other senses. It's what produces the problem of things being in the mode of present-at-hand with spatial measures of visual objects and representations along with Aristotle's series of now moments, a theoretical outlook, ideal modellings, homogeneity and uniformity, static architectures, fixed and abstract numerals, the illusion of separation between things etc.

The two hemispheres of the brain are very different, plus there's also the way the vagus nerve connects with the organs and runs around the body. For meditation to be successful the right brain really has to be dominant. The right brain connects over to the left side while the left brain doesn't run back over to the right side.

The deep slow breathing while the body is relaxed and the mind is quiet ionises the vagus nerve and produces a hormonal cascade from the guts up to the brain. It's felt as heat in the body, like fire. The energy is gathered, matures and transforms the body and that in turn clears the mind.

Literacy creates a roadblock to successful meditation. It literally wires up the body so it can't work. I was pretty much functionally illiterate at school so I think my disinterest with books growing up played a role in meditation having a big affect on me when I first tried it.

You can see here how literacy creates an unconscious (because western/phonetic left-hemisphere dominance shuts it out) -

https://www.youtube.com/watch?v=ZMLzP1VCANo

Preliterate peoples don't have an unconscious. The discovery of the unconscious is actually caused by the effects of electronic technologies, mimicking or stimulating the right brain. So I'm leaning on Marshall McLuhan here... "the medium is the message".

Western philosophy since Plato has simply been a series of reactions to the effects of differing technologies as they come into being.

Now back to the presocratics, my friend has worked out authentic Pythagorean harmonics -

https://www.scirp.org/journal/PaperInformation.aspx?paperID=83684

The key really is the understand that nonlocality is the basis for reality. It's not an intellectual exercise, rather it's a fundamental truth which can be discovered by applying proper meditation techniques. Many saints, gurus, yogis etc have been able to demonstrate paranormal powers and abilities as the fruits of their practise!

Matter is condensed light and pure light is the substance of thought. These things are accessed and revealed in meditation.

Maybe that all sounds a bit "out there", well I only wrote that because you prompted it. I don't go around talking about these things normally for obvious reasons.