https://vignette.wikia.nocookie.net/...20080922004701 FFII Ultima Weapon
https://vignette.wikia.nocookie.net/...20100513170744 FFVII Ultima Weapon
https://vignette.wikia.nocookie.net/...20131214055112 FFXIV Ultima Weapon
I'm not saying that FFVII is the only game with Ultima weapon (I directly said this), I'm saying that XIV is directly influenced by it's design (As is the FFVIII one for that matter, it even has the FFVII sword in its hand). Saying that FFII's Ultima Weapon inspired the XIV boss is like saying that FFVIII's omega weapon inspired the FFXIV Omega boss.
Edit to end an irrelevant argument:
https://vignette.wikia.nocookie.net/...20120506223427 FFVIII Ultima Weapon
https://vignette.wikia.nocookie.net/...20130927194837 FFX Ultima Weapon
Even if we take the two Ultima Weapons that share concepts with the FFVII one, we can see that even they deviate from the design and don't resemble the VII incarnation as much as the XIV one does. The VIII one resembles two creatures fused together, with the quadrupedal half having it's own "face", and the top half seemingly riding this half. The top half is also centralised on the body, which the XIV one does not.
The FFX incarnation is arguable closer than the FFVIII incarnation, removing the two beast element and giving the creature much larger legs in a squatted position. It also removes the wings in favour of large tendrals from it's shoulders.
So yes. XIV's Ultima weapon is inspired by VII, not any other final fantasy, that is very clear to see by just looking at the images.
