1) My sense is that this game is intentionally designed to make it difficult to achieve solo wins on big maps (like 500p map). This capital morale penalty is one such game mechanic. Another is the 'corruption' mechanic. I see this as a good thing because it makes teamwork more important.
2) I think the map is okay the way it is right now. Your point about America having a hard time expanding is true. But this is a 2-sided coin: it is also hard for people to invade America.. So there are pros and cons to this. America is not necessarily disadvantaged by the lack of direct air connection to Africa. .
3) I agree that the lag in late game for 500p map is a problem..