The idea of an Ishgardian ambassador wouldn't have been particularly frowned upon, because we already knew beforehand that they once held relations with the outside world, and certain houses still do under the practice of hiring foreigners on occasion to work with them.
In fact, some people did roll with that concept.
It's different for Garlemald, because it's made very clear that they wish to conquer for the sake of what they consider to be the Greater Good. Regardless, if we were to theorycraft about their internal government, it would be more plausible to assume that it is similar to the later days of Rome, than to make something up entirely from scratch, considering their naming conventions, military makeup, and general outlook towards the world at large.
If we were to assume an absolute parallel with Rome (which it could be argued is unlikely in totality, but considering the way that other city-states are modeled, it is nonetheless likely to be close), then we would be able to assume that those that question the Emperor's judgement would be suspect to immediate persecution by his hand; the Garlean emperor would also be able to refuse any legislation allowing for diplomacy if they willed it, and would also have control over the entirety of Garlemald's standing army.
The question then arises of, if this were true, how come there was such a large dispute between members of Garlemald during Project Meteor? There are several possibilities.
1.) Emperor Galvus's Health. It's implied during ARR that Galvus is ill, and losing grip on his power as a result. We're not entirely sure when this happens, so it's unclear whether his health was failing during the Project Meteor incident as well. Either way, as of HW, he is dead.
2.) Garlean Generals Doing Whatever The Hell They Want. Also possible, but seemingly unlikely, since you'd think that there would be some crackdown on that. At the same time, however, Nael van Darnus was pretty clearly loopy later on in the storyline (and was also seen among members of Garlemald as a little too extremist for anyone's tastes), and Gaius van Baelsar didn't seem to give much of a shit about the "official" abandonment of invasion plans either. This possibility, however strange, may also be granted further potential if one considers that the Garlean public at large was rather opposed to Project Meteor; that's a pretty clear indication of a higher-up somewhere just not giving a shit.
3.) Imperium maius. This is a special kind of commanding authority that was present later on in Roman history. Although some Emperors had greater control over Rome's armies than others, under later forms of Roman government, what made the Roman emperor special was that, despite having the ability to call and end senate meetings (despite having only a little more power than a normal senator, as well as absolute judicial ruling) was the ability to show up on the field of battle, and immediately assume command, so long as he stayed there. If he's not there, then the highest commanding officer that is not the Emperor (usually a general) would have command as they normally would. If Galvus wasn't able to make it out to Eorzea and issue command, it's likely that the Generals were free to do what they wanted by Garlean law of command, or just because no orders made it out to them.
Personally, I would put my stock in imperium maius being the reason. This is because after killing Bismark in HW, we get a prime example of whatever the Garlean version of imperium maius is in action; the newly-appointed Garlean Emperor Varis zos Galvus swoops down, waves his command of his army in your face, shows off his cool airship, and leaves. Despite the presence of Regula van Hydrus, the legatus of the legion you see in that cutscene, it's very clear who the troops are listening to.
If you combine Possibility 3 with Possibility 2, then you'd get the most likely scenario for why that happened, in my mind.
The gist of what I'm trying to get at is that if we're going to theorycraft about Garlean government, the best thing we're likely to get is something that looks like the Roman Empire, which is clearly reflected in the names, army-ranks, etcetera, that Square Enix gives us.
It's also possible that all of this is moot anyway; regardless of whether or not Garlemald is open to diplomacy, Ishgard most certainly isn't, considering that they have joined an Alliance whose sole purpose at the moment is telling Garlemald to F-off. So no matter how much we speculate on what's happening in Garlemald's government, the thing is, we know what's going on with Ishgard's government, and they're not open to negotiation.
In fact, some people did roll with that concept.
It's different for Garlemald, because it's made very clear that they wish to conquer for the sake of what they consider to be the Greater Good. Regardless, if we were to theorycraft about their internal government, it would be more plausible to assume that it is similar to the later days of Rome, than to make something up entirely from scratch, considering their naming conventions, military makeup, and general outlook towards the world at large.
If we were to assume an absolute parallel with Rome (which it could be argued is unlikely in totality, but considering the way that other city-states are modeled, it is nonetheless likely to be close), then we would be able to assume that those that question the Emperor's judgement would be suspect to immediate persecution by his hand; the Garlean emperor would also be able to refuse any legislation allowing for diplomacy if they willed it, and would also have control over the entirety of Garlemald's standing army.
The question then arises of, if this were true, how come there was such a large dispute between members of Garlemald during Project Meteor? There are several possibilities.
1.) Emperor Galvus's Health. It's implied during ARR that Galvus is ill, and losing grip on his power as a result. We're not entirely sure when this happens, so it's unclear whether his health was failing during the Project Meteor incident as well. Either way, as of HW, he is dead.
2.) Garlean Generals Doing Whatever The Hell They Want. Also possible, but seemingly unlikely, since you'd think that there would be some crackdown on that. At the same time, however, Nael van Darnus was pretty clearly loopy later on in the storyline (and was also seen among members of Garlemald as a little too extremist for anyone's tastes), and Gaius van Baelsar didn't seem to give much of a shit about the "official" abandonment of invasion plans either. This possibility, however strange, may also be granted further potential if one considers that the Garlean public at large was rather opposed to Project Meteor; that's a pretty clear indication of a higher-up somewhere just not giving a shit.
3.) Imperium maius. This is a special kind of commanding authority that was present later on in Roman history. Although some Emperors had greater control over Rome's armies than others, under later forms of Roman government, what made the Roman emperor special was that, despite having the ability to call and end senate meetings (despite having only a little more power than a normal senator, as well as absolute judicial ruling) was the ability to show up on the field of battle, and immediately assume command, so long as he stayed there. If he's not there, then the highest commanding officer that is not the Emperor (usually a general) would have command as they normally would. If Galvus wasn't able to make it out to Eorzea and issue command, it's likely that the Generals were free to do what they wanted by Garlean law of command, or just because no orders made it out to them.
Personally, I would put my stock in imperium maius being the reason. This is because after killing Bismark in HW, we get a prime example of whatever the Garlean version of imperium maius is in action; the newly-appointed Garlean Emperor Varis zos Galvus swoops down, waves his command of his army in your face, shows off his cool airship, and leaves. Despite the presence of Regula van Hydrus, the legatus of the legion you see in that cutscene, it's very clear who the troops are listening to.
If you combine Possibility 3 with Possibility 2, then you'd get the most likely scenario for why that happened, in my mind.
The gist of what I'm trying to get at is that if we're going to theorycraft about Garlean government, the best thing we're likely to get is something that looks like the Roman Empire, which is clearly reflected in the names, army-ranks, etcetera, that Square Enix gives us.
It's also possible that all of this is moot anyway; regardless of whether or not Garlemald is open to diplomacy, Ishgard most certainly isn't, considering that they have joined an Alliance whose sole purpose at the moment is telling Garlemald to F-off. So no matter how much we speculate on what's happening in Garlemald's government, the thing is, we know what's going on with Ishgard's government, and they're not open to negotiation.
