This is one of the weirdest things I never seen mentioned. In the "timeline" where Aerith is supposedly not stabbed....why does she still act as though something serious happened to her? Why doesn't she barrel roll out of the way and and attack Sephiroth? She's not groggy from some deep sleep or anything, she's just sitting there, she should be able to just react like a regular human being would when attacked, by going into a fight or flight response.
Instead she sits there for 5 hours while Cloud is holding off a descending blade, and then lies on the floor like she just had a god damn heart attack or something.
I haven't played Rebirth yet (waiting for it to be on Steam, as my only gaming system is the Steam Deck), so I don't know how far off the current lore this question is but...
What if summoning Holy requires taking the life of the summoner?
It wouldn't matter then if Cloud stops Sephiroth's sword or not. Aerith would die anyway, because she would have to give up her life to summon Holy.
Type-0 does this with its summons. The bigger ones requiring the lives of many people to be summoned. An hell if it wasn't gut punching to watch it happen.
Like I said, just throwing an idea out there.