Roman/Byzantine gear is more tenable than kevlar et al. because Roman gear is not OP alongside current cRPG gear. cRPG has, for a while now, been about gameplay and roleplay. cRPG roleplay, the devs seem to have decided, is an individual affair. It's up to individuals to make their own specific aesthetic styles, matching things like Milanese armour with an Italian Sword or deciding to completely mash diverse cultures, times, and looks. Though it may be immersion-breaking for hardcore roleplayers to see samurai fighting hoplites, the devs have decided that they won't burden the majority of players with the onus of one specific RP setting. Instead we get a diverse set of vaguely medieval european armours, middle-eastern themed gear, and East Asian stuff too! In this context of personal imagination driving roleplay, rather than an isolated in-game setting, I don't see a reason not to include historically based non-op/gamechanging gear.