That's a very interesting comment, because I think a lot of it stems from how you interpreted Remake from the get go.
One of the big things about Rebirth was that it pretty much deflated Remake's ending, because Remake's hook was 'now we are off the chains of fate, good and bad consequences of that will have to be dealt with' but in Rebirth the consequences of that were... almost nothing. Every character followed the fated path laid out for them anyway, so breaking free from Fate ended up being very similar to not breaking free of fate.
See, the problem I think with Remake's ending is that people literally ignored the warnings the devs had been saying since the announcement of the project: this remake is the OG with an expanded story and inclusion of the Compilation. And they have been saying this over and over again, but fans
chose to ignore their words.
As a result, for me who didn't have this kind of expectation and who, after playing Remake, was absolutely certain that they were following the OG major points, Rebirth hit exactly where it was supposed to. I said it here again and again that Aerith would die for example, that it was written in Remake - not about the plot, but about how they treated her (think about Nojima saying she had to make an impression because she was going to quickly get transferred: the formula did not change, and it would've been pretty unfair to Tifa to treat Aerith this way if she didn't die, because it would've been favouritism, which it wasn't).
Maybe the fan backlash steered them away from it, or maybe it was all part of the plan, but either way the central hook of the last game seems to have been abandoned or at least pushed to the sidelines. Which raises the question... if they did that once, how do we know they're not going to do it again for part 2's hooks?
I mean, it was their plan from the beginning... Nojima wrote literally an outline of the whole story from beginning to end (I don't remember which dev talked about it, I read way too many interviews sorry). They didn't abandon anything, they went on with their original plan.
One of the interviews that really marked me wwas after Remake when they said they considered
the Wallmarket to be a big deviation of the OG. To me it showed clearly where they thought they could go, and what they ignored (Remake's ending). And I've said it here, but Remake's ending leaves us exactly where the OG leaves us at this point so...
The Whispers in Remake were mostly coherent, they did things for reasons, but in Rebirth they don't seem have coherence to what they do. Some of them are now working for Sephiroth, some of them are now working for the Planet, but some things they do don't line up with either of them. We needed some kind of reveal as to the nature of the Whispers, not necessarily the full picture, but some progress towards understanding them. There were plenty of opportunities to discover something new about them over Rebirth, but we didn't. The team travelled through three massive repositories of knowledge in Cosmo Canyon, Nibelheim, and the Temple, but didn't discover anything new about them.
There were already whispers that seemed to be a little different in Remake and people theorised that they were working for Sephiroth/Jenova. Hoever, it is true that the ending
modified things, with Sephiroth clearly taking control of a lot of them.
Starting there, we have Lifestream White vs Lifestream Black, and it makes sense whithin the world of FFVII (On the Way to a Smile Sephiroth and Aerith' chapters, notably, established this, and this is heightened in Rebirth). I personally think that they are explained by the Gongaga chapter but hey, who am I to dare look at a Tifa scene uh. We have been literally TOLD that the Whispers are following the Planet's wish and given their colours wwe can tell that they're either following the Planet (or maybe Aerith! The one who's dead in the Lifestream...) or Sephiroth, and there's nothing surprising about it given the fight between Aerith and Sephiroth in OtWtaS.
Schroedinger's Aerith is an excellent way to crack Cloud's head open when he finds out.
Aerith's death was done that way to show how Cloud dealt with the death of people dear to him. When you see her death, you know that it's exactly what happened with Zack; he literally made a new reality where Zack didn't even exist so he didn't have to deal with his death. It's exactly the same here.
Now I do hope to see the real Aerith's death in p3. To me, that solemn moment is clearly missing. Cloud won't crack his head, as he'll have to deal with both her and Zack's deaths and accept his failures. This is the main theme of FFVII, which is loss and how the living deal with it. After the denial, the realisation and acceptation.
I have low confidence in the Wutai stuff. I get they needed to make the Huge Materia quests more central to the main story, but the game ended with Rufus and Sephiroth agreeing that the whole war is a pointless distraction. It's a shame because Yuffie's characterisation is genuinely superbly done, but Rufus v Sephiroth is a tough conflict to get invested in if neither of them are taking it seriously. Rufus can't lose while literally playing both sides, and Sephiroth can kill him literally any time he wants.
For the Wutai stuff, what gives me hope is Yuffie. I think her characterisation and the hints that were given about her and what's happening in Wutai are great, so I really think it's about sticking the landing there. I guess we'll have to see. I hope it'll be great, but yeah, they can totally fail it too.
It's really weird that Sephiroth is treating Rufus the same way he treats Cloud. If Cloud and Sephiroth's relationship is not unique, that has major effects. Rufus can even somehow see the Whispers, he's like, being elevated to co protagonist even though it's important to the story that he not be.
For Rufus, the problem is exactly the same, his fate is tied to how they will do Wutai and connect him to it. I think he gained in importance because of Wutai, and it's really the story there that seems to have a really big importance that will tell us if it's a failure or not. Also, I feel they want to connect his character there versus how he is depicted in ACC, to show the fall of a man who had everything. I guess we'll see.