Yes, it doesn't make sense. Your theory literally contradicts everything we know about the situation and relies on making assumptions that are contrary to what the movie shows.
- Stelline says it's illegal to use real memories -- but you want to assume she did anyway
- Stelline says there's a little of the artist in her work -- but you want to assume she just put an entire memory of her own in, unaltered
- Stelline says she is the best because of her imagination -- but you want to assume she used a completely unaltered, entirely UN-imaginary memory
- Stelline says she does this because she wants replicants to have happy memories -- but you want to assume she gave them a very UN-happy memory
And there is no indication whatsoever that anyone else has that memory, I don't know where you're getting that from.
IMO it's just a bad bit of forced writing -- just a way to have K 1) think he's the child and 2) meet Stelline and realize she is the child. Without the illogical scenario of K having that memory, he never would have gone to Stelline and never would have known she was the child even if he had gone to her.
You're being kinda obtuse here.
Her saying it's illegal to K is completely irrelevant, and says nothing about how she really thinks about implanting "real memories". There is probably a rule/law against implanting real memories, but she's not going to say she shirks that rule to an LAPD Blade Runner, is she? This also partly explains why she says "it's a real memory" in an as circumspect a way as possible. But why she felt like she had to say that it's real to begin with is internal reasoning that we as the audience are not privy to. It could be explained by her wanting to connect with someone over something though. Or just an in the moment thing. Why did Deckard open up to K about Rachael when he's a Blade Runner that could potentially mean to do him harm? We don't know, it's one of those things.
Her saying "there's a little of the artist in her work" is a statement much more in favor of her implanting one of her own memories than it is proof against it. It can literally be directly interpreterend as her tipping her hand.
And again, the memory is not an unhappy one. It's a triumphant one, as Joshi says. "Fighting for what's yours". Unless you're going to tell me that they give replicants only happy memories? Remember, she just makes the memories. Wallace corp implants them. I don't think they blindly implant everything the memory-weavers hand over. (Also, you should really watch Inside Out if you think unhappy memories are bad!
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And her having a great imagination does not preclude her from wanting to connect with the outside world (or even subconsciously with her own kind, sorta kinda) by sharing her own story. I'd say you have a point if this were the only argument, but there's too much going against it.
Besides, all of this totally plays into the "what is real" theme anyway. What's the difference between a real memory, and one that's made to be real? The only difference is that the actual real memory is one that's been lived.
Perhaps they've literally been inside her code.
Note that Mariette finds out K has a Joi when she first meets him. Then somehow when Joi called her over she knew she was going to K's and came ready to bug him. And most of Joi's actions after Mariette meets him push him to find Deckard, even playing up the special angle that Freysa said the others had felt. And after they find a wounded K they break the tracker to hide the evidence of manipulation. And you know they are manipulating him when Freysa pushes him to kill Deckard, telling him his sacrifice will prove his humanity.
Even Joi's moments of independence are in favor of Freysa's group. Telling K to break the antenna comes after Mariette planted the bug and has a means to track him. And breaking the home device prevented both the police and Wallace Corp from gleaning anything from her about the child or the investigation.
So the line means they've literally been inside her, and maybe that she really doesn't have much there and any sense of sentience is truly an illusion.
I didn't get that impression, I'm more with Zakalwe on this. But it does sorta kinda fits, in terms of the pure mechanics of it? I don't think that's what they meant for us to get out of it though.
But then again, I do think it'd be kind of a stretch to assume the resistance could so elegantly reprogram an AI to do exactly the things they need her to do. I think the AI in this universe, like the replicants, kind of are open-ended. In that humans built them initially with a strict purpose, but the replicants/AI exceed that purpose simply due to emergent behavior.