[SPOILERS] Stormblood Ending

[Theodric]

We've killed some Imperials for a better weapon to defend hearth and home with.

No. They were deliberately hunted down, killed and had their very aether and souls transferred into a weapon. A weapon that was then used to kill other Imperials - which could very well have been friends and/or family members of those horrifically reduced to nothing more than extra power for a weapon of mass destruction. Eorzea isn't even the Warrior of Light's home, anyway. He just happens to have aligned himself with factions that focus almost entirely upon it.

If a Garlean had cut down Lyse, transferred her life force into a gunblade and then used that power to put down Thancred the narrative would be very different no matter how it ended up being used.

Thankfully Zenos is not entirely representative of Garlemald as he openly denounced it through both his own words and his own actions. His father, too, wrote him off as a monster.

It's also not a competition as to which side is 'worse'. What matters in the context of the discussion is that both sides have crossed lines and neither has the moral high ground. It would be a different matter entirely if one side had been presented as having absolutely no redeeming qualities but that isn't the case at all and is only relevant for individuals such as Zenos who...aren't actually serving Garlemald but themselves.