Perhaps the greatest cutscene of all time: Genesis v Sephiroth

[Sephiroth]

Well first off, I don't count anything in the Compilation as canon

But the "reality" of Final Fantasy VII does not depend on you. And it does count. I do understand your thoughts. Originally Zack was shot by some kind of back attack. But it would have been ridiculous to show this scene in Crisis Core since Zack is as strong as Cloud. So he just defeats an army and weakened of the battle the last few ShinRa soldiers - which represent those who were seen in the original flashback of Final Fantasy VII - kill him. And for a character who was the one Cloud thought to be a back attack death is not really great.

the Cloud who enters the Mako Reactor at the beginning is physically the same as the one that fights Sephy at the end in terms of capabilities, he doesn't gain the ability to take more hits or kill people faster.

Leveling and damage output has no bearing ever in a story, and I will never understand why people can't seem to understand why both need to be treated as different circumstances. I don't believe Ultima in IX does 9999 damage, I know it can seriously smurf my party up cause I did watch it level the surface of the planet and I can't fathom how anyone would survive that.

Actually not. It is true that game mechanics to not count. Only the scenes in battles do count as well because they show what the characters are able to do but Cloud and the others get stronger in battle through experience like all other humans do. Not to forget that Cloud has a sleeping superhuman power. He was planned with that and it is always unleashed when Sephiroth starts to be arrogant and makes him angry. With that power he always succeeds in defeating him - except when all the heroes fight together.

Sephiroth has so many abilities. If Square would let him use them all at once there would be no necessity in telling a story. You need to give the heroes a chance as well. It is the same with all stories with super villains who are way stronger than the heroes. Actually it is almost always that way in Final Fantasy.

But you have already admitted partly with that comment:

Even Kitase and the Ultimania makes it perfectly clear that Sephiroth is far greater than Cloud and anyone else for that matter, and that both defeats are caused by Sephiroth underestimating Cloud. Hell, chances are still possible that Zack is stronger than Cloud.

We will never be able to say if Zack is "stronger than Cloud". What do you mean with that? Zack's will is stronger than Cloud. Yes. But there normal fighting skills were made equal and since Cloud has copied Zack with Tifa's memories and replaced Zack's life with his own, it is not even a wonder, that he is that good.

it wasn't about basing the film in realism (like how some cells can make Kadaj into Sephiroth)

That's perfectly realistic. Sephiroth just needs some cells, if not only one to reunite himself - that's not clearly said. Sephiroth's reunion is mixed with the shapeshifting ability. The reunion he did in Advent Children was nothing else as shapeshifting JENOVA's headless body in the ShinRa headquarters and controlling it so he could do what he wanted and reunite JENOVA as well. But Sephiroth's reunion is way stronger than the original reunion of JENOVA. JENOVA needs its head as center. Sephiroth can activate the reunion just by willpower. Of course in Final Fantasy VII-1 he had JENOVA's head as well. But I am talking about his own reunion. And that is stronger than his own. He even thinks in the lifestream about just using the power of "his mother" to come back, et cetera and with the memories of the others, escpecially Cloud's, he can fully reunited and shapeshift back to his normal form.

I don't believe those are wings though, they are two masses of flesh and organs that happen to be justting out of her back, for all we know, its actually her fileted back muscles from Hojo and Gast experimenting on her. As for the Calamity from the Sky bit, that has more to do with the fact the game specifically states she came to VII's world via meteor as a transport. She's a calamity and she came from the sky via meteor, hence the name.

We never get to even see her true form, for all we know she doesn't have one since she shape shifts. I also don' see how shape-shifting as a Cetra to infiltrate them is going to work if she has "wings" jutting out of her back.

It was never clearly said that JENOVA really came on a meteor even though it is likely. The Cetra thought a meteor fell and when they arrived at the crater they found JENOVA who looked like a Cetra. It was not mentioned if there really were parts of a meteor. Even in Advent Children it was not clearly said by Sephiroth because he said "What I want, Cloud, is to sail the darkness of the cosmos with this planet as my vessel. Just as my mother did long ago." but it is not mentioned if he just means that he wants to travels through the cosmos like JENOVA or if he wants to travels through the cosmos on a destroyed planet like JENOVA. The line is not clear enough because both is possible.

And yet - YES, JENOVA likely travelled on a meteor. I just mention what the lines are.

And you did see JENOVA's true form. JENOVA Synthesis is JENOVA's true form. It is just not 100% perfect since Sephiroth, Cloud et cetera have JENOVA cells but the Ultimania itself says that this one is the one closest to her true form. And that is no wonder. With the reunion you shall fuse your cells to get back your normal form and JENOVA SYNTHESIS/COMPLETE/ABSOLUTE is meant to be that form: A giant tick-like alien with two tentacles and a female-looking body since it fits the story.

By the way - JENOVA's sealed cetra-like body was already mutated. It is no wonder and has not really to much to do with the experiments. JENOVA was fighting the ancients when they found out that it is no Cetra and of course the game itself should just show that it is a inhuman, alien-like being. And the things should definitely remind of wings. But not because it is the Calamity from the Sky. And Sephiroth's wing is not a normal wing like we all know. The original "one wing" also looks just like a mutation - but more wing-like as JENOVA's. But not even close as the normal angel wings he has. Of course because it should look special. By the way - the wing of Sephiroth was not just shown as a mutation because of JENOVA cells. It was thought (for Sephiroth, not for Genesis and Angeal) to represent that he is incomplete since he was interrupted during his metamorphosis. He would have been "complete" by absorbing the whole lifestream.

I do understand your thoughts. But it is, how it is.