> What doesn’t make sense to me is how it’s possible for it to be an illusion that anything is being experienced at all.

It might not make sense to you now, but that's because of what we know or what we think we know, today (hence my ancient Greeks analogue). Look at the Gazzaniga effect, people seamlessly make up an "experience" narrative out of absolutely nothing. Whatever experience was claimed there probably didn't exist prior to the point of questioning, and then was wholly manufactured. Thus, that particular experience was a fabrication.

> If the experience is illusory, then who/what is being deceived?

Why does there need to be a who/what being deceived for something to be an illusion? A mirror functions regardless of whether someone is there to pretend there is a soul in it.

We come from a race that took two thousand years (after it was first proposed) to accept the brain as the seat of the mind, over the heart — just because the heart physically reacts in times of emotion, while the brain remains inert.

Whatever the truth is, humanity probably won't know it until enough generations of the old guard indoctrinated in the old ideas have passed on.