I don't get it, either. Their arguments hinge on Aerith's supposed happy ending - she wanted to live, you see. Why are you pushing Aerith to be dead together with a rando she doesn't even love anymore - you must hate Aerith and Zack! She wants to be alive with Cloud.
When you ask what happens to Zack in this happy scenario, crickets. If lucky, I'll get something like oh he can be alive too, just with Cissnei. Or no sorry, Zack is a side character we can't bring back everyone, that would ruin Cloud's story. Like dude was brought back just to learn about Aerith loving Cloud now and presumably to play some kind of role in the LS sequence, after which he can dissolve back to nothingness. Zack's main purpose is to bring Cloud and Aerith back together, you see. Cloud then supposedly rescues Aerith, she puts his mind back together, they defeat Sephiroth, and Tifa eats grass at CA's wedding just like she deserves. That's about the gist of their vision for p3.
The gaslighting going on is insane. Today for example, I learned Loveless doesn't have anything to do with Zack. Cloud caught the reunion petal during NPTK, Zack let's it go - checkmate he's letting go of Aerith. I mean Cloud caught it when he is playing Alphreid - this is significant. When he's not Alphreid, he doesn't want anything to do with the reunion pin in the dream date despite being told to play along. Aerith accepts it by herself. Zack is then shown a few minutes later chasing the reunion petals (not letting them go). Let's not forget the man is basically tied to Aerith's church with an umbilical cord - that's where he's always coming back no matter what in all media since like ACC and Crisis Core. Ever Crisis is reluctant to even show him anywhere else in promotional materials. And I won't even attempt to make sense of what hardcore CAs desire for Tifa - I've heard Emilio and Johnny mentioned.
These people aren't serious. The game has taken on a new dimension in their heads. I get it at some leveI, I too thought after Remake the story could go differently. But after Rebirth, I can't see anyone thinking that in good faith. Seems like setting yourself up for major disappointment and whiplash.