for the defensive slots. You may think a bigger nation has better defensing capabilities
But think about it, let's use Fraggle Rock as an example. If someone decides to attack him, it would be a nation in similar size, basically another Fraggle Rock sized nation and both sides are in war range of each other (similar capabilities)which doesnt make any difference than two 1-city-newbies fighting each other
If the slots are based on capabilities, it'd be unfair to the old players
Even if the score range is increased to +100%, it would still be unfair to the defender. Let's say Sphinx is the defender since he has 41 cities which is close to 40 cities as you've mentioned. Ten nations that have half the capability of Sphinx all raid him at once. That would mean Sphinx is outnumbered by five times and that would not be fair
Extra resources should also have a use instead of just sitting there for no reason
Extra units seem interesting but should have special capabilities as mentioned up there about stealth planes
Nuclear disarmament: Don't think any alliance would follow that as once another Global War breaks out everyone's nuking each other. Would just fail like the League of Nations after WW1
City cost: If cost are the same and price only increase when you grow it, people would be spamming 1k infra cities since there's no need of getting the infra high up if any city costs just 225k
Stock market: There actually are stock markets in banks and corporations made by players