What's up with Bahamut?

[Beddict]

Let's see... since I am in love with lore info gained from battle content... (though Enkidoh already did an exemplary answer).

Midgardsormr's Simulacrum as Recorded by the Omega Weapon during fight on the Dragonstar:

'Tis the fate of all dragons to shed one form for another. Even in battle mine assaults are ever changing!

That fact, combined with the fact that summoning/creation magic is inherently difficult, and then further combined with the fact that clearly Dragonkind was new to it... yeah, it's not hard to see why Primal Bahamut looks different from actual Bahamut in FFXIV. I say that dragonkind is new to it, because at least the First Brood were. If dragons had creation magicks, then Midgardsormr did not teach them to his children.

Also worth looking at Ehll Tou, the dragon involved in the Ishgard Custom Deliveries, since she helps further prove your point by backing up what Midgardsormr's Simulacrum says. Near the end of the questline she undergoes a transformation that allows her to better old crafting and gathering tools, and the other dragons involved the quest point out how different she is. From An Ode to Unity:

Ehll Tou:
Ah, I knew you would recognize me! Still, an explanation may be in order...
You see, a dragon's growth is dictated by forces both internal and external. Sometimes this growth can be quite...dramatic, as you can plainly see.
Truth be told, I had been feeling out of sorts lately, but now I see that that discomfort was merely the new me trying to break free. And now here she is─a dragon reborn!

Hautdilong:
Oh, I'm so glad you're all right. More than all right, by the looks of things!

Ehll Tou:
This new tool is wonderful! It's as if Master Arvide knew I was on the brink of incredible change!
Had I received this hammer but a day earlier, I would have held it clumsily in my tiny claws. Now, however, it feels like an extension of my very body. My mind is brimming with the possibilities of what I might craft next!

Dragonet:
Your growth is unlike aught I have seen before! Such a spectacular transformation has already made you the topic of much discussion among dragonkind, and I imagine not a small amount of jealousy.

Dragons are capable of a hell of a lot of adaptation as they grow, and there are many types of dragons we come across in game. Just look at Marcelloix in The Firmament, he's a dragon that stands upright and doesn't really have any wings which is way different from the First Brood or the generic Western type of dragon a lot of people are familiar with. I'm not surprised that a large group of Meracydians of all different shapes and sizes involved in the summoning ritual spat out a Bahamut Primal that looks vastly different than First Brood Bahamut.

[Bright-Flower]

Even if primal bahamut actually looks exactly like the original, it still wouldn't really be that weird to me. Though I don't think we've actually seen the original at any point have we?

[Grimr]

Like it was said earlier bahamut is a bastardization of the real one. The real one was killed during the third astral era by allag. The one 5.4 and 5.5 is lunar bahamut which looks far worse. It doesn't even have a head just a bunch of swirling branches. Lunar ifrit looks more accurate.

The primal bahamut is fought in the final coil of bahamut.

[KaitoAsaha]

I know we just got done dealing with aspects of time travel, and it can be a very easily ruined thing to explore, but I'd like a raid tier or something that deals in us getting to actually meet or fight the primals in their most original form.

Also for a lot of these primal? Did they actually exist or are some just purely folklore or legends?

[TheMightyMollusk]

Aside from Bahamut, Enkidu, Thordan, and the Bozjan queen whose name escapes me just now, we have no irrefutable evidence that any of the primals ever actually existed beyond folklore before being summoned.

Good King Moogle Mogg is a strong maybe, since he's just a bigger moogle; Ravana's physical form seems to be based on an Allagan construct (seen in the Fractal Continuum as a boss), but it's never really addressed; and Susano may or may not count as a primal at all, if there's any real difference between a primal and a kami.

And Alexander is a weird case, because the primal is based on the folklore based on the primal because time loop shenanigans, I don't want to think about it too hard.

[Enkidoh]

Good King Moogle Mogg is a strong maybe, since he's just a bigger moogle;

He's more than that - he was revealed during a Moghome quest that he was actually the first chieftain of Moghome (Chieftain Moggle), and the story about him "dropping a golden rope" to let the moogles escape to the surface is a cultural memory of the transporter between Halo in Mourn (in the Dravanian Forelands) and the Churning Mists - he even had a personal guard that the Mooglesguard were based on.

So the moogles on the surface remembered this historical figure in a somewhat vague and haphazard way, they knew he was a monarch, that he pressured moogles to escape by using a 'golden beam/rope' transport them to the surface from a place high in the sky when an apocalyptic event occured, that he was attended by seven guards/retainers, and that he had 'Moggle' in his name, but that was all they knew, and after the 'Paragons' visited them, they pretty much filled in the blanks, resulting in King Moggle Mog the XIIth.

Personally I think this was to finally put to rest the questions at the time still surrounding him about whether he was a 'Primal' or not, given he wasn't considered a god, which is what the meaning of Primal was meant to represent, but it did make it clear that his whole story was based on a real historical figure.

And of course, we saw this idea further continued with Shiva's real history.

[Cleretic]

Aside from Bahamut, Enkidu, Thordan, and the Bozjan queen whose name escapes me just now, we have no irrefutable evidence that any of the primals ever actually existed beyond folklore before being summoned.

Good King Moogle Mogg is a strong maybe, since he's just a bigger moogle; Ravana's physical form seems to be based on an Allagan construct (seen in the Fractal Continuum as a boss), but it's never really addressed; and Susano may or may not count as a primal at all, if there's any real difference between a primal and a kami.

And Alexander is a weird case, because the primal is based on the folklore based on the primal because time loop shenanigans, I don't want to think about it too hard.

Alexander is a BAFFLING mess of time travel paradoxes, because what you forgot to include is that he's also based on the Enigma Codex's descriptions of an impossible machine (which may itself be based partly on the folklore). So it's a primal, based on blueprints for a machine, based on folklore, based on the primal. And then of course we have to add in the Tycoon, which is a machine, based on the primal, based on blueprints for a machine, based on folklore, based on the primal.

All that just makes you look back fondly on Ifrit, who's literally just 'angry fire god'.

Although some other amendments: The Queen's name is Gunnhildr! Also, speaking of Ifrit, there is mention in the Tales from the Shadows stories of a fire spirit in the days of Amaurot named Ifrita; it's not clear if or how she's related to modern Ifrit, but there's clearly the hint that she is. Also, Susano is a primal, but is one created entirely by accident, based on the kami.

[Beddict]

Aside from Bahamut, Enkidu, Thordan, and the Bozjan queen whose name escapes me just now, we have no irrefutable evidence that any of the primals ever actually existed beyond folklore before being summoned.

Garuda is another one. The Ixal are a chimera race created by the Allagan Empire originally known as the iksalion, and designed as soldiers for the Garuda Airborne Division led by a female general. The iksalion were indoctrinated to unfailingly obey specific individuals, and it's presumed that their indoctrinated loyalty to the female general eventually became worship, their past fading into myth as the general became known as Garuda. Azys Lla also faded into myth after the fall of the Allagan Empire, and is now the Ixali promised land, Ayatlan. Source is the quest An Unwanted Truth and Encyclopedia Eorzea Vol. I Page 249.