It may sound dumb and stupid, but I have a suggestion in regards to adding a new unit for Britons.
This Briton’s new unit will be the “War Chariot”, a powerful ranged cavalry unit with low movement speed but slightly higher health and piercing armor as well as movement speed than skirmishers, and it also turns into a Woad Raider, an infantry, when killed. (Strong vs. infantry and archers. Weak vs. spearmen and camel riders.)
In other words, it is a mobile skirmisher in a chariot with both a Woad Raider as a rider as well as a Konnik’s function in it.