Ehh I've always found the CA insistence that Zack can be bumped off by Marlene quite funny, sounds like a lot of copium. I think it just speaks to how dearly they wish CC and the Compilation were never a thing and he was still a "minor" plot device.
Unfortunately for hardcore CAs, Zack is not trivial enough to be turned into a CA toady by a 4 year old child, especially when he doesn't even have the context on how Cloud and Aerith met.
If CA is going to be a thing, Aerith is going to have to break the good boy's heart in person. Zack has earned that much, at least. Does anyone seriously think this will happen? After she learns the truth of all that happened with Zack? They want to fire the gun from Marlene's shoulder and hope Zack accepts because they know what would happen to fan perception of Aerith if she rejects him in person.
It's a fundamental misreading on the game due to being blinded, imo. They didn't bring him back and give him the setup they did to have him be rejected in the end. He might have had very limited screentime but they made it count. I'm seeing a lot of love for ol' Zack and his single minded insanity (he is truly insane, imo) to get back to Aerith at any cost. The contrast of Zack willing to go to any length vs Cloud's treatment of her through the game is especially stark, imo. Cherry on top, most of the Zack stuff happens during the dream date.
The game wants you to root for Zack and no less a character than Elmyra has gotten attached to him. Not to mention the sheer level of corny involved in Zack and Aerith scenes (ribbon on his hand, gazing at the sky at the same time, touching across the lifestream, taking out a helicopter to retrieve her, flowers healing him reminiscent of the CC DMW limit break, mimicking speech patterns). I would not bet against that level of cheese, personally.
At some point you just have to understand what the game is trying to beat you over the head with and it ain't CA.