These are solid wonders, but slow. The impact that they have on your city is significant, but not until they are leveled quite high and I've found that focusing on military wonders will advance your city further faster.
What's noteworthy about these two is that although the MtH has a much larger footprint, unless you have very few factories the mountain halls is actually more efficient. Obviously, the more factories you have the greater the difference.
Sheet1 Based on end of chapter 11 normal buildings. I factored in everything I could think of, including roads, culture, pop, supplies. Not included is the pop you get from the mountain halls as this was originally intended to compare with the Golden Abyss Just change the number of buildings in ...
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It's important to note that the population boost is based on your working population which for an efficient military city is much lower. Having event buildings produce goods means fewer factories and more military means fewer goods are needed as well.