I kinda get that, I mean, when Aerith sat on the water tower in Nibelheim I definitely felt some measure of "how dare you stand where she stood!", and I absolutely hate the whole "no promises to keep" thing, but Crisis Core also had Zack make a promise to Aerith underneath the water tower, and that never bothered me despite it essentially also copying something that's supposed to be between Cloud and Tifa.
But the reason being upset about it feels so hollow to me is simply that Cloud mimicking Zack, and Aerith seeing Zack in Cloud was always a canonical part of the OG, so when a prequel then shows it more explicitly it just makes me think "what did you expect".
Essentially this.
Yeah, I know it wasn't elaborated on too much in the OG....but nothing was. It's a pretty barebones game that you run through pretty quickly. The bond between Aerith and Zack might not have been elaborated on much, but neither was the bond between Cloud and Aerith. They meet, have a date, she gets kidnapped, talk in gongaga and cosmo canyon. Another date, asks about future, gets beaten up, dies.
The vast majority of this bond is what we imagined, inspired by things like what you said, her being a bubbly pink girl, him being the brooding MC, etc.
What we knew about Zack was that Aerith talked about him during her first date, was upset at her death in Gongaga, talked about him again during their second date and mentioning how she saw Zack again in Cloud. We then find out that the reason she saw him in Cloud was that Cloud was literally pretending to be, and we see Zack Saving Cloud and Talking about Aerith. That's more than enough to allow the player to imagine a bond between Aerith and Zack, especially considering that the implication that Clouds bond with Aerith was in some way a reflection of her bond with Zack already being there.
Again, I get why they're upset, I just think they have no one to blame but their own assumptions. Ultimately I just find it hard to sympathize with the complaint that the prequel about a game where Cloud acts like Zack, shows that the things Cloud did were similar to Zack.