People don't want a greyer light for Garlemald because some of us enjoy being in the antagonistic group, share similar ideals or whatever other possible reasons but just because it makes a more interesting story generally and makes sense, no political power in this world is created by 'evil' ideals from the main parties point of view, there is ALWAYS another motive and the whole 'conquering for pleasure' I doubt that's an actual reason as a whole. Also not many seem to remember Garlemald doesn't just wipe a countries culture slate, they preserve as much as they functionally can with their own society as mentioned in a lore panel.

Garlemald chose to have an emperor based on the bio for solus on the official site, so my best guess is when we do focus on Garlemald we are going to learn their history and what prompted them to go on the war path. We know very little about it's people or it's culture and history so all we can do is wait and see what SE has in store.