Justicar is part of the Arclight line
I just wanna get this out there to anyone who tries to talk about Aatrox's Ascended form compared to his Justicar skin. The Justicar skins are a variant of the Arclight line. Nothing more. More importantly, that was his on-release skin. Why does that matter? Because on-release, the one and only Darkin had no relation whatsoever to Shurima. His background was intentionally unclear because they didn't put him into the bigger story yet. Not only did the concept of the Darkin being fallen Shuriman Ascended not exist at that point, but also
**SHURIMA DIDN'T EXIST AT THAT POINT. **
So there is no possible way it could be related. And even with the new model, they simply made it mirror the old look. They didn't give it the gold wings he had in the lore, and didn't change it to be like it would if it were supposed to look like his Ascended form. They kept it a justicar skin because that's all it is and ever was.