Continuation discrepancy: Why did the gurus lose their magical abilities?

Part 6 of this series from Walter about various major discrepancies in the Continuation compared to Miura's Berserk.

[373+374] Why did the gurus lose their magical abilities?

In episodes 373-374, it’s explained that Skellig’s magic users, including the great gurus, have lost their power ever since the island was destroyed.

Puella’s translation of Episode 373:

Serpico: The witches have lost their base and most of them are losing their power or so. Fortunately, we’re visitors that came from outside of the island. So we haven’t been affected by the disappearance of the island, I think.

This development appears to be a contrivance invented to write off the newly introduced magic users, for which Mori and Studio Gaga seemingly had no plans. Now that they have arbitrarily had their powers stripped from them, I don’t expect to see them for the remainder of the series as more than extras (if that).

The problem is that magic doesn’t work that way in Berserk. Magic users don’t rely on some well of power in order to do magical things. There is no mana pool. They apply their deep knowledge of the world and its inhabitants and establish pacts with astral beings. They can visualize phenomena beyond the corporeal world and can coax its inhabitants into a mutual coexistence with humans. It’s like an extension of science for a magical world. They study it and its inhabitants and learn how the rules and properties of the world can be manipulated.

When Schierke explains to Farnese one of the fundamental concepts of magic in Episode 249, she says: “Magic is not accomplished merely by reciting a spell and drawing symbols. It is the chaining of images in conjunction with those things that first yields efficacy. The essence of magic is the world of thought, and it is practiced in the astral world”

The destruction of the cherry tree in Elfhelm, while tragic, should have had no effect on the magic users’ abilities to understand and thus conduct themselves through magic. If there is a barrier that prevents them from applying their knowledge, then it hasn’t been properly explained.

Compounding this discrepancy is the fact that Serpico says this limitation only happened to certain people—the island’s inhabitants (“Fortunately, we’re visitors that came from outside of the island. So we haven’t been affected by the disappearance of the island, I think.”) In the last episode that Miura worked on, Episode 364, he established that Farnese, Schierke, and Casca had been accepted as inhabitants of the island through a ritual.

Puella’s translation of Episode 364:

Danan: The casting ritual to make you three become inhabitants of the island has been accomplished. Above all else, everything here accepts you.

Schierke: We… have been accepted…

If they were accepted as inhabitants of the island… then why didn’t they lose their powers, too? These lines are in direct conflict, and it doesn’t take a genius to determine why. Having incredibly powerful magic users like the great gurus is a big variable to work with when planning the ending of the story. It’s likely Miura hadn’t fully divulged their import and role for the remaining portion of the series. So, they were conveniently written off with a hasty solution that isn’t consistent with the previously established rules for magic, or the very recent development of Farnese, Schierke, and Casca being accepted as inhabitants of the island.