Sorry for the belated response, but I thought about this a bit before I went to bed. Altdorf's population is plausible. Cologne in the 1400's had a population around 40,000. Frankfurt, Aachen, Nuremburg, and Munich had populations in the 20,000s. Hamburg had a population of around 20,000 in the 1400s and passed 100,000 in the late 1600s.
But I don't believe that dwarf Karaks are the equivalent of human cities. My hunch is that dwarfs are generally more likely to live in the hold itself, or very close, rather than more spread out like humans. That raises the question of where all their food comes from, but that's a separate discussion. In the end dwarf's likely have a much higher urbanization rate, and that a hold is more equivalent to a province than it is to a city.
Urbanization in Early Modern Europe was somewhere in the ballpark of 10-20%, so Altdorf having 80k could imply Reik land had 800k, though there would be large number of small to medium sized towns strewn across Reikland, making itss total population much greater. Paris in the 1400s had a population of around 100,000, but France (smaller than modern France) had a population between 10 and 15 million, I believe. Given the proliferation of Jade Wizards and priestesses of Shallya, I could see Reikland having a population a bit shy of 10 million. And that generally follows what I've heard that Sigmar's Empire is decent amount more populated than the Holy Roman Empire was.
Now, I doubt there would be any dwarf hold that has a million inhabitants, but a hold with 40k dwarves would definitely qualify as the low end.
