Originally Posted by
MikkoAkure
We're going way off tangent, but besides being accused of regicide, he's also a deserter. He can talk his way out of the accusations around murdering Varis since the lead witness and actual perpetrator is a traitor, but he 100% deserted his legion to pursue a personal vendetta against the Ascians and then started feeding information to the Eorzean Alliance. You'd need to rewrite elements of the story going back years to make Gaius a valid candidate for the throne.
While they could have introduced a Larsa-equivalent, it was a bit late in the game to do that and we'd just be repeating the same story as FFXII all over again. Just because it worked for one game doesn't mean it will work for another or needs to happen again. Regardless, Garlemald is neutered and can't really do anything large scale anymore. The writers left the fates of the remaining legions vague if they want to use them again for something, but we also might be stepping into territory the game has already been before if they have yet another rogue legion like the IVth or the VIIth. Legati and princes vying for the throne ended up destabilizing and destroying the country so it's probably best that they do away with the throne anyway.