You just admitted, Aerith decided to go alone, and that's what strikes me as terribly selfish and stupid. Imagine if Yuna decided to say to her guardians "screw ya'll, I'm going to do this pilgrimage myself".
I think that Yuna would. That is, if at some point Yuna realized that Tidus had somehow become the group leader and center and yet Tidus is a mythomaniac liar who attempted to strangle her, possibly because he is actually controlled by the enemy, say if once or twice Seymour gave orders and Tidus fell in trance and obeyed. Especially if Tidus has thrown a speech hours before, about getting a certain mass-destruction weapon before Seymour because Seymour has so many mindless slaves who could throw their life away to get the weapon for him, and then it is demonstrated that the mindless slave was none other than Tidus itself, who did in fact provide the mass-destruction weapon for Seymour.
Among all this, Yuna is also in love with Tidus, or what she perceives to be Tidus.
Yes, I think in such circumstances Yuna would distance herself from Tidus immediately. In Yuna's case the group is more connected to her than to Tidus, in Cloud's case is the opposite. Another reason to do exactly what Aeris did.
For as much as I utterly prefer Tifa, selfishness and stupidity hardly are traits of Aeris. Would nullify the whole story if they were, actually, since Aeris ultimately saves the day.
You know, I've spent most of my teenage and twenties saying that FF7 was an overrated game and undeservedly overshadowing other JRPGs but I'm in my thirties now and looking back, it's surprising to re-discover how foreseeing, vast, cohesive and deep the narrative was. I think most people don't even realize it fully. Which brings us to the next:
I don't mind the timeline shenanigans, I think it breathes a lot of new life in this story. I can see why it would annoy purists, but to me, it sort of feels like I'm experiencing something with more weight, as a sequel. It sort of makes me feel more connected to the characters and story more in a way.
I have an hard time realizing how you could think that Zack&co returning to life is a problem for the story themes and meaning and yet not despise the very same narrative device that made this insult of a plot twist possibile. A lone chapter was enough to destroy most of the FF7 themes all in a single shot, I am amazed about how lightheartedly people are taking this.
And purism have nothing to do with it. Screw Purists. But who are purists anyway? Nobody denies that the game was flat-out great because, and not despite, its differences. There were a lot of things that where entirely different in this FF7R, and all for the better. Biggs, Jessie, the Avalanche, Wutai, the Turks, Wall Market, Beautiful Bro, Honey Bee, Hojo's Lab, Barret. All different and revamped, and all utterly awesome. Why? Because they took the original and made expanded, modernized and re-imagined takes of it.
Chap18 is a different beast. It's spitting on all the themes that gave the story meaning and impact, and turning them to a childish Kingdomhearted narration where death, time, tragedy, effort, self-conscience and even ecology are all meaningless. And it was possibile with timelines and broken destinies. If that's what you call breathing new life in a story, well, you certainly are an happier person than I am right now.