It clearly is, but to play Devil's Advocate...
... while Gaius had sympathetic motives on the surface, deep down he was little more than an ambitious, power-hungry conquerer like the rest of the Garleans. He had standards, and a point that Eorzeans likely turn to gods because they're not strong enough to accept hardship, but ultimately the reason he wanted to conquer Eorzea was to prove that he could do so. (It's also why he opposed Project Meteor, as using a cataclysmic weapon of mass destruction to lay waste to the land would leave nothing worth conquering.)
The Ala Mhigans are belligerent and ill-tempered, but that's likely a product of their warrior culture, and having their homeland occupied likely just makes it worse. Driving out the Garleans and repatriating the Ala Mhigans won't solve all their problems, but it would be a step in the right direction.