This is more of a question/suggestion than a issue.
Is it possible to control the density of a city? If they are shaped like a circle, it would be good to concentrate the skyscrapers in the center and the smaller buildings at the edges.

How can I simulate this situation? I believe this is the best way to create realistic cities.
Perhaps mixing the predefined rare cities, with my previously mentioned approach using chisel blocks.

You can control this with cityChance and some of the other city parameters. Check those out

Here is some info about the algorithm used:
https://wiki.mcjty.eu/mods/index.php?title=Basic_Structure

Thanks!