Ok, so you're assuming that a different set of circumstances is the "normal" state. Doesn't make it any more valid. If anything, the map shows us that all of the Western Continent is less divided that it was when Tarquin was defeated, so how is the casual observer supposed to determine that the Empires of Blood, Sweat and Tears are the aberrations?
You're still assuming, baselessly, that it's trivial for a casual observer to recognise continuity when the empire changes. Actually, for some reason you're selectively applying this only when the countries are near each other. When they're in different areas you're just assuming they'll "expand independently" without considering what that entails. The con as described by Ian and Tarquin relies on all three countries working in concert, they simply don't have the option of "expanding independently" if they want to avoid precisely the pitfall Tarquin was trying to avoid with the scheme in the first place. Remaining hidden from people who are unlikely to notice them in the first place is not more important than enacting the actual plan!
Long lives and a stable yet geographically close location. Yes, the Elves are ideally situated to notice this one particular clue. It's still pretty circumstantial though, and the Elves are, in Hinjo's words, "slow to go to war". I really must stress that the strongest thing in Tarquin's favour is that nobody is looking for a grand Machiavellian scheme underlying Western politics. Not one that works, anyway. The clues are only worth something if someone is willing to examine them.