I'm writing Wyrnurg into my stories now. An empty king. One man who lost his kingdom, who has nothing to lose yet he refuses to give up his land and his customs.
If you don't want the traits mixing, you should do this with different species. Since these 4 were all human, they could have kids together, even when they are on different kingdoms.
The thing about the health kingdom is that since everyone is the same species, they don't need to actually kill anyone. They can just stand around their enemies land to capture them, something they are really good at since they are near unkillable themselves.
I don't think it's very confusing that the attack speed guys lost to the health guys. If it takes 1k attacks to kill a single healthy guy, and they deal 2.5 damage back per attack, they're going to kill a guy with 100 HP before it kills them
The problem with an attack speed buff is that a 99% increase to attack speed is just under doubling your damage output. That health buff seemed to be significantly more than doubling, even without the damage reduction being bypassed by weapons, they just didn't stand a chance.
A race with a higher base damage (making the damage down more impactful) and high base health (making the health increase less impactful) should balance those two out more.