Il Mheg 1/2 of two mirrored zones?

[Iscah]

As well as the paradoxes of time travel will case a calamity in of them selves too.

Where are you getting that from? I don't recall it being stated anywhere.

As I recall - would have to double-check, but from memory the issues with Alexander were firstly the Illuminati's plans to go back and rewrite history in their favour, and secondly the inherent danger of Alexander existing and draining the land of aether, even if its power was used "for good", so it sealed itself away "in time" to prevent that.

Apples and Oranges both fruit but not the same thing...

I'm not even going to try to argue your fruitbowl analogy.

But it's still not proved that Grani is "ours" just because it's not a cash shop item.

If you exclusively receive it from an "out of game" source, whether purchased or preordered, that means we don't receive it from a source within the game.

Our battle chocobo is ours - we received it from the GC when we signed up.
The black chocobo was a gift from Haurchefant.
Maggie the magitek armour came to our rescue in Castrum Meridianum.
The manacutter was built for us by the Ironworks.
Midgardsormr agreed to carry us once we proved ourselves worthy to him.
We earned the right to ride a Yol in Bardam's Mettle.
That ridiculous Starlight bear apparently just followed us home after we bonded over throwing presents at gaudy treants.

Those are the mounts I earned from quests. They have stories behind them. You can only ride them once that individual character reaches the logical point in the MSQ where they receive or gain access to it, and everyone gets them equally. (Give or take "equally" for the seasonal mount, but equal for everyone who was able to complete that quest.)

If a Grani Horn drops into my inventory as a special-edition gift, when did my character earn the right to ride such a thing? Why did my not-special-edition-purchasing friend's character not earn the same right? How has my Lv20 alt character acquired this creature when he's only barely earned his chocobo licence?

Making it a collector's edition mount makes it less likely that it will be ours within the course of the story, unless it's a different version of the creature somehow. (Though I'd be pretty unimpressed if I'd wanted the mount, paid extra to get it, and then we get practically the same thing within the game as well.)

Been in the aftermath of a intense forest fire before? grey and black is about it.

But it's a black-and-white image. (With some blue highlights, but clearly not "true to life" colour.) The picture is drawn in black and grey regardless of whether the things represented in the image are black, green, brown or purple. Compare the colouring on the girl - she looks like a white ghost, not Minfilia as we saw her in the trailer.

And even as just a silhouette, those undefined background shapes look like something more solid than burnt-out trees.

Yes its an oddity.
Have you asked yourself is there another reason for it that could explain it in game?

No, because the creators have said it's done for the sake of consistency and not having to update scripts to reflect the passage of time.