There's nothing outright wrong with Spartans wearing Corinthian helmets, depending on the time frame. It'd be better to have them in pilos, but it's not essential. It's daft enough having them in at all as any sort of playable faction in the game period, but i suppose they're cool, so they might as well be given shiny helmets as well.

Athenian Thureophoroi are a nice surprise.