That it's not actually Oversimplified at all; rather it's simply that the story and/or narrator have not bothered to get too bogged down in the weeds of how Magic works, most of the time, in the face of good Storytelling. I mean, I respect the crap out of Tom Clancy, but sometimes he'd wax on and on about random details of military procedure or geopolitical history, to the point where you'd forget what the actual scene was supposed to be.
To say it was Oversimplified in the beginning implies to me a retcon, the idea that thing worked differently in the earlier books and the rest was added on after-the-fact. But just about everything that we've been talking about here is stuff that Harry mentioned to one degree or another in the first few books (other than stuff like Mantles and the Gates that were specifically saved for the latter Arc).
But remember that we're getting it all from first-person narration, and Harry is specifically
not infallible, nor are his sources, necessarily.
For ex, Harry tells Karrin early on that the Fallen can't possess you without your permission. That's what the Council teaches, and Harry believes it.
Several books later, though, it turns out that this isn't
quite true, just usually. Michael tells Harry that yes, one of the Thirty
can take your body against your will, under certain circumstances, I think Michael said that drug use could weaken you enough for it to happen, or participation in certain occult rituals or activities could open you up to involuntary possession, there may have been some other things.
So Harry wasn't
wrong in what he told Karrin way back when, just not entirely right. He had an oversimplified view, and maybe so did the Council.
Another example: throughout the early books, Harry thought the Outer Gates were a metaphor, not a real
gate. Now he 'knows' that they are real gates, physical, material objects...except of course that he's got it oversimplified still:
2015 Grid Daily interview
The Gate seems like something that, if it didn’t start with a consciousness, would develop it over time. Is that the case?
It probably is, but the consciousness of an inanimate object like that is mostly like that of a mountain. “I AM HERE.” And it’s just increasingly aware of its here-ness. The Gate actually exists very differently than what Harry saw, but that’s how Harry has to interpret it because it’s far out in the Nevernever. Your mind has to put things into terms it can understand or you go squirrely. Harry’s got a very good mind for reducing things to simple ideas. Which most of the Senior Council would say with a roll of their eyes.