I'm not talking about the basic fact of disliking the WoL. I actually loved the Garleans hating the WoL (more people should do it! dunk on my character and their protagonist powers! i welcome it!) I'm talking about the repeated instances of them deliberately choosing self-destruction over a chance for survival for themselves and their family members; of buying into the ideology to the point that they sincerely see the death and destruction of their country and loved ones as a better option than "submitting to the savages" or being "corrupted by magic." That one-sided understanding of what drove the wars with Garlemald that you describe is also a form of propaganda - Garlemald (again, as a nation, the general populace are largely victims of circumstance and manipulation that almost anybody would be vulnerable to if immersed in - it's part of what makes things so difficult) has very carefully nursed a persecution complex that also makes them just flat-out refuse to engage. I would say the same thing about a country pushing the line that the Garlean people are just wicked and evil and oppressive, denying the history where they were oppressed.
I strongly disagree that Garlemald is an instance you can point to as "it's all the twins' fault and the narrative blindly buys into their idealism," because the actual sequence of events in Garlemald was about demonstrating the opposite. They failed repeatedly - they failed to convince the sisters, they failed to understand the mindsets and the (sometimes futile) effort to talk through the indoctrination, they failed to judge Quintus properly multiple times, culminating in his suicide. And they explicitly blame themselves, repeatedly - as recently as the Omega quests - for those things. Even in the present era, Garlemald still has holdovers who refuse to accept help all over the zone, and the twins are having to continue putting forth their efforts.
Yes, there are times when Endwalker's shallow shounen-idealism gets very tiresome, but not so much with Garlemald, which was a pretty grim, difficult part of the scenario. More like the actual climax of the story at Ultima Thule, I think.