Problematic notion about Zone 5 & 6 story bits.

[LilimoLimomo]

That said I never thought that characters from ARR to Endwalker would hold such strong beliefs of what you can and can't do with a soul.

Oh, 100%. It's one of numerous ways that Dawntrail's narrative is flawed. Because since ARR, we've been doing all manner of occult madness with souls, such as injecting thousands of them into our relic weapons. And suddenly someone has a problem with how souls are being treated? Yeah, it sounds hypocritical, it sounds ethnocentric.

To be clear, I don't think Living Memory needs to be shut down because it's bad to use souls or whatever*; it's entirely about them needing to harvest an endless amount of energy from other living creatures to sustain their own existence. Like the ARR Primals, they gotta go.

*though since ARR, I have very much raised an eyebrow that everyone is cool with harvesting souls like that...

Had Sphene not presented her ultimatum and started the interdimensional fusion, we would have 100% tried other solutions to keep these memories "alive".

I don't think we would have; at some point in the story in Living Memory, one or more of the Scions state that from the very beginning, Living Memory was doomed to failure because the system's design is unsustainable. Quite simply, Living Memory is computer storage that needs to be able to infinitely grow (to hold more data, more memories), and the bigger it gets the more resources it will require to keep the lights on. But nothing can infinitely grow; it's not just a fact about nature, it's a fact about reality. Resources are finite, and thus infinite growth is always doomed to failure; infinite growth cannot be sustained. I think it's a bit poetic that in reality, the only natural phenomenon that attempts to infinitely grow is cancer.

The writers were correct to have the Scions point this out...though they were sloppy in having the initial engineers of Living Memory fail to realize this incredibly obvious flaw in their system. Any engineering team worth their salt would have noticed that problem well before the project was finalized, and any population that truly loved their dead wouldn't have generated simulacra of them that would need to choose between their own existence and destroying all life throughout the universe. It's a glaring plot hole.

I could argue that the Aetherial Sea is just a different version of Living Memory, they just operate differently with different sets of beliefs.

At least according to the lore we're given, it's not; the Aetherial Sea breaks down things like souls and memories so that they can form new life, and that life will eventually be broken down itself, and so on and so on. It's the circle of life. But Living Memory just keeps the souls and memories so that they don't return, and thus new life can't be created from them.

And again I have to emphasize, according to the lore we're given, the simulacra in Living Memory are just computer simulations. It's not an afterlife, it's a room full of ChatGPT bots that have each been fed memories related to a specific dead person so that they can impersonate them.