It's worth pointing out that Garlemald, the Republic, was around for 600 years before it became an Empire... and that it was onlywith Emet-Selch... basically sabotaging it by design that it became an Empire to begin with. So, somewhere there's some set of laws for what Garlemald's Republic was like... and those laws seemed to have more or less worked for a good long while. Taking Garlemald back to those probably wouldn't be the worst way to have Garlemald end up.
Pre-HW Ishgard was not a Republic. The people making all the decisions for Ishgard was the Four High Houses and the Church; it was very classiest with the richest people making decisions for everyone else (which is why Ishgard has so many stories about economic classes mixing not being a good thing). It is only in post-HW that Ishgard has become a Republic. So if anything... both Isghard and Ala Mhigo are following in the old Garleian Republic's footsteps with their governing styles. There's some irony there for you.
My thing with Gaius is... he really has no reason to know anything but the Garlean Empire's way of thinking, and yet somehow, he does. Doing the math shows he was born two years after Garlemald became an Empire and it would have been in an military expansionist state for his entire life. And I really don't want to think about what growing up in such an environment (think of the propaganda!) would have been like from a Garlean's pov when it comes to... basic things like human decency to people who aren't like you. I'm honestly more surprised that the biggest overall issue with Gaius is that he's culturalist rather than that he's racist. Because I legit don't know where he would have picked up the idea that racial differences don't make any real difference, but cultural differences do (the kicker being that cultural differences do matter, just not in the way Gaius thinks they do). The vast majority of other Garleans we meet are really racist and Gaius somehow isn't (anywhere near the degree they are at least). And Gaius is older than every Garlean we meet too (except Emet-Selch). If anything, you'd think he'd be worse about all of that stuff than the other Garleans we meet.
I honestly really want to find out more about Gaius' backstory before he became the Legatus of the XIVth Legion, since... he's not as bad as most other Garleans are in a way that makes me think something happened to him to make him think differently enough that he can be reasoned with at all. It's kind of like hearing about someone who grew up from childhood to adulthood in Nazi Germany but somehow didn't pick up on the idea that race mattered, but culture did. Which is to say, it makes me want to know how/why they came to that conclusion because that doesn't sound like what you'd expect to happen in that situation.