Third Age: Reforged is a mod for Medieval II Total War, that aims to overhaul the multiplayer aspect of the Third Age Legacy, by thoroughly rebalancing the units and factions while also implementing tons of new content, maps, units, etc. (NOTE: campaign is still in development)
nahhhhh the old castamirs chosen felt much more authentic, these replicate Gondor too much. Although Umbar technically is a subsidiary of Gondor they wouldn't copy their armor styles.
Why wouldn't they? Gondor's style is essentially Numenorian and the Black Numenoreans of Umbar are supremacists lording over the Haradrim, so it seems unlikely that they'd abandon their identity entirely.