I do not recall the story claiming that the people who used the earring suddenly changed drastically as people, or did things that they would not endorse on reflection. They were simply, from a black-boxed perspective, more charismatic, intelligent and less prone to akrasia. These are, IMO, good things.
The story says neither that the people who use it change personality, nor that their personality stays the same. It’s agnostic on this point; it only says that their lives are “unusually successful”.
When I read it, I took for granted that the Earring has some kind of consciousness or personality separate from the human using it. We know this because it’s able to to speak in its “own voice” to Kadmi Rachumion. Plus, as you’re correct to observe, the story doesn’t make much sense as a parable if the Earring just extrapolates its character from the human it’s attached to.
I think the thing that makes the Whispering Earring creepy—which also makes the mind Claude is trying to be, or at least might try to be, creepy—is the combination of:
It has a hyper-accurate model of what will make me happy
It is unilaterally better at fulfilling this reward function than me, to the point where anything I add to its advice is essentially superfluous
It is not just a more capable or intelligent version of me; its mind isn’t shaped the same way mine is
There are lots of aspects of me that seem to have importance to my identity, but probably aren’t strictly necessary to make me happy. If I let the Whispering Earring take over my agency and make decisions for me, it will only remain ‘in-character’ as me for as long as doing so maximizes the reward function. If an out-of-character choice would make me happier, better for me to have that character instead, right? Better, in the long run, to have whatever the mannerisms of a hypothetically ideal person in my situation would be. I suspect such a person doesn’t look like me at all. Once I’ve reached the point where I’m letting it control my individual muscles, though, would I even notice if it started ‘breaking character’? Would I notice anything beyond an ongoing series of reward signals and twitch reflexes? Why would I need to?
(Note also that even if the Whispering Earring doesn’t have its own personality, Claude definitely does. So to OP’s point, having Claude’s agency directly substitute for yours would very, very definitely change your outward personality.)
I’m skeptical that this is true, or at least that it could be confidently predicted to be true based on our current understanding of intelligence. My understanding is that the human brain is much larger in “effective parameter count” than even the largest LLMs (although there’s no 1:1 comparison of neurons to parameters), such that even if my laptop has enough electricity coursing through it to emulate a human brain, it hasn’t got anywhere near enough VRAM. It could be that both AIs and humans are systematically inefficient in some way that, if we understood it, could allow us to produce a more capable general intelligence at <1% the scale of either. But I’m not sure why one would expect this, or what principles imply it.