The great political blame game that is Shinryu....

[GrizzlyTank]

The only reason the primal was a dragon was due to the Final Fantasy Omega/Shinryun reference they pushed in. Everything lorewise ingame pointed towards Rhalgar "the destroyer" being the primal even though we already had a primal in rhalgars image (Ramuh lord of levin). And the eyes being used to summan a primal doesn't mean that it has to be a dragon as seen with mega-pope and the knights twelve.

[Hinoto-no-Ryuji]

The only reason the primal was a dragon was due to the Final Fantasy Omega/Shinryun reference they pushed in. Everything lorewise ingame pointed towards Rhalgar "the destroyer" being the primal even though we already had a primal in rhalgars image (Ramuh lord of levin). And the eyes being used to summan a primal doesn't mean that it has to be a dragon as seen with mega-pope and the knights twelve.

This, of course, is the out-of-universe reason, but I think they did a good job justifying its form while simultaneously using it as a chance to expand the lore surrounding Primals as a whole: a Primal summoned not as an avatar of any specific deity, but instead for a broad purpose, using not dedicated and focused prayer but instead desperate and disparate dying wishes and cries. The reason it was a dragon, I'd wager, is that the most specific anything got form-wise was Ilberd (the chief summoner, remember) directly invoking the Dreadwyrm of the Calamity. I'd posit that the eyes had nothing to do with it. And as for Rhalgr: it was only the most likely candidate because of a total lack of others. Ilberd never came off as being especially devout to Rhalgr (does he even ever utter his nation's patron deity once in all his dialogue?); in addition, among those dying, only a single soldier says the name, and even then only in the English version, as that same dialog is just crying out for power to strike back at those killing him in Japanese.