Read both parties' comments, and I actually am strongly backing the idea put forth by Ikram. Giving a population a cap, and allowing individuals to disperse that population among their settlements. Allowing the lore minister to make exceptions to those wanting to exceed the cap, with evidence they are making something truly iconic and worthy of exceeding that of other realms.
What is the point of every city having a huge 1million pop? It isn't special then. The only way to keep something unique and incredible is to gatekeep otherwise we'd all have it.
My only comment is that large realms underneath the surface are not inherently dwarven. Not important to the topic, but it's a comment, definitely.