Yes I know most of the factions have same military uniforms in that time period but then again this is just a game so making generic generals of different factions have different uniforms is nothing too out of hand; hell even that Ma Chao guy has crazy anime armor. This will increase the appeal to play as different factions other than just having different heroes, color or locations, etc.
You don't have to give generic generals too crazy looking armors. You can just give them some unique, realistic looking armor for each faction (maybe recycling some of the heroes' armors). I am sure this will increase the appeal and reason to play as different factions without lore-breaking.
This is just my little suggestion for you guys to consider.