stuff
Sorry, I misread the start of your original post. For the record, I want a system that makes expansion vs. development an actual decision in the short term.
But the late game shouldn't have paper leviathans like early 20th century Russia. The way game mechanics work, the early game is like the USA expanding westward and spreading its culture without any long-term degradation in per capita wealth or technology, and the late game is like a dozen different USAs, all coming from the same starting position, taking broadly interchangeable planets and populations from each other (except for xenophobes). This is not EUIV or Victoria, and there are no mechanics to represent countries being ridiculously ass-backwards compared to others, for deep-seated cultural or historical reasons.
If everyone starts equal, tall-and-small countries should never be so comparatively tall that they can wreck countries that are significantly larger than them.