If I thought Jim kept good notes and was actually aware of what he had written over time I might give more weight to what he says versus what he puts on the page. It's one thing to write a six book series, quite another to write a 26 book series. Is this point in dispute?
And that's why I don't say you are wrong, but instead that I'm of a different opinion and only
think you are wrong.
But whatever talents the Fallen have act through their hosts connection to the coins. They don't imbue any permanent change in the host. So if a host uses magic given to him by the Fallen then if he puts down the coin does he retain the magic?
A problem with coming to any firm conclusions on this one is that we really only have Harry's experience with a shadow and Cassius's aging. Cassius's magic doesn't seem to be any different than when he had the coin. He just doesn't have eternal youth and the Denarian battle form. Harry had a couple of things from Lash that are gone and some things that aren't. He doesn't have a photographic memory or the ability to understand and speak Sumerian or Etruscan. He does have the pain management technique. (I know I'm leaving stuff out). So we know some things stay and others don't. Cassius's aging is actually an example of both. If the advantage went away immediately, he'd be like the guy who "chose poorly" from Indiana Jones and the Last Crusade. If the advantage just stayed, he would have started aging normally, not at an accelerated rate.
So what do we do with this? We guess. I tend to think that if Marcone has the coin for long enough, and he practices magic long enough, he will develop as an extremely skilled minor talent. I don't think he'd ever have a lot of juice (excepting things like eating ghosts for power), but I do think he'd develop something.
I do think Marcone is the type of person with a strong enough will and the planning skills that he will extract enough information from Namshiel that he will be able to get along without the coin. Both methods of acquiring an independent source of magic and, if he holds the coin long enough, a source of eternal youth. Marcone isn't one to remain dependent on any one source of power.
Nothing in the books really explains how magic talent really works. Is it a muscle everyone has to some degree? If the supernatural was widely known, would most people be
very minor practitioners?
Same with the circle for Butters in Dead Beat, once Harry showed him how to make it, it didn't take much to power it.
At first, you'd think this would answer my question, but it doesn't. It's Butter's blood that powers the circle. A practitioner can power the circle with the power of his mind. In the strictest sense, Butters is doing magic, but I don't think that qualifies him as a practitioner.
one popular theory is that Vadderung trained Merlin. I mean he certainly didn't go to Hogwarts. Vadderung has only given one thing up for free.
It's stated in the books that Merlin was taught by Odin. I can't remember if it was one of the legends listed by Harry about him, or something Eb said. If Eb said it, I'm going with it's about as confirmed as anything else in the books.
What was the only thing that Vadderung gave up for free? He gave Harry some free advice in Changes and then he helped at Chichen Itza. (On a side note, just because Harry doesn't pay a price, doesn't mean it was free or without a price. Like how Harry doesn't always pay a price for Lea's help because Margaret did).