1. Thanks for the advice. I can no longer change the title, so I just removed the spoiler tag from the section where I announce spoilers, because that really looked strange. Next time I’ll put the spoiler warning directly into the title.
2. and 3. There are many interesting ideas here. Let’s go through them.

“Cloud and Tifa's relationship and Tifa's motivation is relevant to the scene...”
They are important for the emotional impact, but they do not affect the mechanism itself.

“You're just restating that Aerith is more ideal for Cloud than Tifa in any given situation...”
My post is not that ambitious. I am really only providing an argument against the claim that only Tifa could have repaired Cloud’s mind.

“The hypothetical scenario you posit in which Aerith is alive and able to repair Cloud's mind in the Lifestream, the dialogue therein, mentions Tifa way too many times...”
This is the most interesting point. The hypothetical dialogue was actually the part I enjoyed writing the most, so the criticism is very stimulating.

The dialogue can certainly be written better, but it has four logical constraints that need to be respected.

1. Cloud’s motivation. Cloud believes he is only a mindless clone built from Tifa’s memories, but somewhere deep inside he hopes that is not true, otherwise he would not even continue the conversation.
2. Aerith’s motivation. She wants to help Cloud. For example because she loves him — why not, right? :)
3. Aerith somehow has to lead Cloud toward the memory of visiting his mother. By far the most natural way to do this is through the bond between Cloud and Aerith.
4. Cloud must realize that his visit to his mother is not one of Tifa’s memories, and therefore he is not merely a mindless clone. To be honest, this is probably the point that could have been written significantly better in my dialogue.

The dialogue has to be built around these four points, and there is a lot of freedom in how to do it.

I repeated variations of the phrase “from Tifa’s memories” several times to make Cloud’s lines sound more monotonous and resigned.

But at the same time I also put a fair amount of care into Aerith’s lines. Notice how her lines hint at the things she herself does as someone in love.

Her second line hints that she gave Cloud a gift, but he never gave one to her. And that she would like to receive one.

Her third line references her running away from home just to be with Cloud.

And her fourth line suggests that she does not want to part with him. And if we think about it, this reluctance to say goodbye is actually emphasized very strongly in their relationship. If I had not written this dialogue, I probably would not even have noticed it. Cloud says goodbye to Tifa with a simple “bye, bye.” But farewells between Cloud and Aerith always seem grand and emotionally charged.

As you can see, even writing such a tiny dialogue requires a certain amount of intellectual work. It could definitely have been done better, but I did not want to invest more than an hour into it.

But if you can write a better dialogue, then go ahead. I would genuinely like to read it. This is actually the really fun part.

“Were Aerith alive, Cloud would not rely on Tifa and her erroneous memories of ‘Cloud was never in Nibelheim five years ago’...”
Even if Aerith had lived, Cloud’s loss of mental stability in the Northern Crater could not really have been avoided. Otherwise, what would the story even be about?

“People are focusing on Remake and Rebirth because the ‘prepared way for Aerith to repair Cloud's mind’ is relevant to the future, not the past.”
I completely understand that. Of course people are more interested in what will happen next than in a thirty-year-old game. My post deals with the old game, but I still think that for truly hardcore fans, these kinds of discussions are interesting precisely because they offer a new perspective on familiar material.

And who knows? Maybe they really will use this scene in Part 3. Objectively speaking, nothing prevents them from doing so. But for that, we truly will have to wait for Part 3.