You dont build WW in Kingdoms. Its Legends, where they try all kind of new things. They even have 5 Tribes and now they are Beta testing 6th. Kingdoms is still stuck with 3 Tribes. You could also argue, that adding new Tribes adds Imbalances in the game and nobody wants them. But some people get bored to always play the same tribes, and want variety.
Thanks for proving you haven't even played through a single round of Kingdoms. If you did you would know there are WWs in Kingdoms too. You should play a few rounds and become proficient at the game before suggesting a complete overhaul of the game's design.
Making a balanced game is easy on paper, but in reality, the more complexity you add the more difficult it becomes to keep things balanced.