Hot take: HP killing people indiscriminately shouldn't be considered genocide since they are deity, not a human
First of all, I’m not defending the HP for nuking the entire poor nations. Especially if you imagine yourself as an ordinary person in Teyvat who got obliterated for something that isn't your fault, feels unjust and unfair.
But I have seen a comparison of Planes to hitler, nazi, zionists, or other war criminals countless times, which is not a fair comparison because HP IS NOT EVEN HUMAN 🥹 HP is literally their deity or demiurge, they literally control the lives, fates and souls of same people they CREATED.
By that same logic, we do not call natural disasters like earthquakes and tsunami a “genocidal” because it doesn't follow human rules. We do not label the grim reaper a killer simply for taking souls. These forces are not judged by human standards because they do not exist within human systems of right and wrong.
The same applies here. HP and the Shades are celestial entities. They are not bound by mortal law, nor are they written to care about human concepts of justice or morality. Whether their actions are cruel or catastrophic from a human point of view does not automatically make them “criminal” in the way a human dictator or war criminal in rl life would be.
For example, if I am a dev, I can delete my own characters whenever I want. Other players can not call me a murderer because those digital characters are just pixels on a screen for me. I am their creator, and I can do whatever I want with my creation. Celestia sees the people of Teyvat as lesser creations in the same way, a mortals who are gonna die and reincarnate again by HP anyway.
Now, imagine if an actual human like Dottore or Rhinedaughter repeats HP's actions, then yes, that would absolutely be genocide. Because humans are accountable to human ethics, morals, right or wrong, but applying that same standard to higher deity-like entity is honestly so stupid.
Although, yes, they are colonizers for the poor dragons.