The funny thing is that imo Kazuha's face doesn't look as similar to Aether's than other characters of his body type. Obviously the only things that differentiate in Genshin are eye shape and colour. So, you have to answer me: Why is his face extremely identical in a way that Xingqiu's, Chongyun's, Albedo's, Razor's and Xiao's aren't? The big eye faces are: Aether & Xingqiu. The more adult faces are: Kazuha, Xiao & Albedo with Chongyun & Razor being kinda in the middle. Eye shapes are slightly differnt overall for everyone with Razor's being the closest to Aether. And last but not least: Imo Diluc's eyes and hair look closer to Kazuha's than Aether's by far. Both character's bangs intersect in the middle, messy hair and same hair length (aside from the pony tail). Aether has only one of these, but oh the hair colour is closer, right? Worry not for Diluc has the same eye colour! (and an eye shape that is more similar as well)
This is why your "extremely identical" feels absurd to me and it feels more like it's "at first glance he looks similar" because messy hair + same-y hair colour. Doesn't help that some people mention it all the effing time and the bandwagoning has started, but I take my Canadian Diluc and you peeps can do whatever with your Canadian Aether from a Genshin Impact that I don't know of. :P