You're not the only one; everyone here points out that it's the girls' affection that goes up or down, and how comfortable they are with sharing moments with Cloud based on those points. It's not about Cloud's affection, it's the girls' affection that change there.
I see this a little differently.
Despite the undeniable romantic tone, I think the purpose of the two main dates is to establish important plot points,
especially Aerith's one that's the only scene that directly points out the similarities between Cloud and Zack and the fact that he may be hiding something about his identity. I believe this is the reason why she starts with the highest amount of points. As regards Tifa I think that her attempt to talk to Cloud is linked to her version of Nibelheim incident, more than a love confession, which is something that she already tried and failed to do before.
The aim of the Highwind scene, imo, is to close Cloud's character arc. He retraces the three points of the Lifestream sequence and renews each one of them:
The promise ->
After all, I promised. That if anything were to ever happen to you, I would come to help.
Finding the truth together ->
Someday we'll find the answer. Right, Tifa? That's what I learned from you when I was in the Lifestream.
Tenders feelings no one can ever know etc etc ->
Hey Tifa...... I...... There are a lot of things I wanted to talk to you about. But now that we're together like this, I don't know what I really wanted to say... I guess nothing's changed at all... Kind of makes you want to laugh...
After that whether they just hold their hands or summon Chokobo chicks is their own business!
The alternative scene is really apathetic it...doesn't add anything to the story, it doesn't say anything about Aerith and it doesn't fulfill Cloud's character arc in any alternative way. I think it's also worth mentioning the fact that the musical theme is not Tifa's theme, Aerith's theme or any romantic song, but "On that day 5 years ago".
Sure the low affection scene is canon as well but it's definitely the weakest one under any perspective.
Cloud's subconscious encourages Tifa to reveal her feelings to real Cloud (
Tell him what you told me, later. He'll probably be so happy) and the dialogue on the Highwind in Case of Tifa links up with the high affection scene. It makes reflect about what the player has to do in order to fail to achieve the 50 APs, and how according to the Remake Tifa already has 50 points.
Ah there's also an interesting discarded scenario about the ending cutscene (I have no idea if anybody ever mentioned it in this forum, I'm rather new here!). Instead of the "meet her there" line the original dialogue had to be:
C: We're going home, Tifa...
T: Huh?
C: We have something we need to do when we get back. We haven't...seen the other side of the mountain.
T: Yeah...let's go home.
(Ultimania Archive vol. 2 pag. 108).
It made me realize that indeed in that scene Tifa falls from the cliff like during Mt. Nibel incident but Cloud saves her, and meanwhile plays Tifa's theme. It also makes sense that in ToTP the death of Cloud's father is related to "the other side of the mountain" as well. I don't really get why they had to change it but this dialogue really completely closed Cloud's arc. Enough to debunk the "Aerith is Cloud's Promised Land" stuff anyway!
Why every time I click on a twitter link I have to see a DOKI DOKI ??