Valley of the Marauders

I want to understand why the opponents are stronger on the Barbarian than on Remixa's stream, and why you can't build anything from the advanced building branch in the city?

Okay, you're introducing some confusion into my map. Difficulty is a subjective concept; maybe you have a different build, which is why it seems more difficult...
As for building something, you can build everything, except for the tavern, I think.