Aether's actions towards Mondstadt were particularly cruel compared to what he did to the other nations. Though he executed all the other nations government, Mondstadt seemed to be hit harder than all the other nations in Teyvat. But considering how the current Mondstadt came to power and what Aether is doing right now, it makes sense. Barbatos became one of the Seven after he helped the people of old Mondstadt overthrow their tyrant God and despite a few hiccups here and there, there was peace until Aether came along. Looking at what Aether has done so far, it makes sense that Aether was particularly nasty towards the City of Freedom. Their entire history is essentially based off of overthrowing an immortal tyrant, which is what Aether has become. Where eventually Decarabian has failed, Aether planned on succeeding and decided to do everything in his power to ensure that the people of Mondstadt would be unable to come together and fight him.
Mondstadt was the biggest threat to his reign because Aether is essentially mirroring what Decarabian was doing before his untimely death.
Veer claims during a tense shouting match between Lumine and himself in an Insurgency Meeting that Lumine couldn't give a damn about Teyvat or the rest of them. The only person she cares about is Aether, who happens to be the one making everyone in the continent suffer. Which makes sense. Ever since Lumine woke up in Teyvat, she has learned and witnessed for herself that her brother has become an evil tyrant. And when Lumine comes across people the more she travels, the more they often see her as Aether's sister and constantly make unfavourable comparions or deride her. Not to mention that when Veer makes this accusation, Lumine hasn't been awake or working alongside the Insurgency for very long compared to having been and traveled with her brother for centuries. And people like Veer hardly sway her to their side. So between her brother and Teyvat, it would make sense that Lumine cares more about her brother due to just how people treat her solely for the fact that she and Aether are twin siblings and that she hasn't had enough time to grow attached to others.
