Actually, y'know one thing that I was reminded of: GDI vs. Nod. For real, GDI is very Purity, while Nod is very Supremacy/Harmony, at least style wise.
- GDI is very human-centric, with a military styled after more classic conventional armies, with extensive use of power armor for its more advanced infantry. They are also highly opposed to the alien substance that engulfs the planet, and are actively fighting for its removal.
- Nod, meanwhile, is intent on gaining power through any means possible, whether its via advanced cybernetics or its advanced bio-modification via extensive use of same alien substance. The style of Supremacy/Harmony's units also have a certain Nod-ish vibe to them when you think about it.