Balance does not matter as much in the single player arena, but I will add that in my last 3 EA games Vanheim was the last remaining nation versus me. But the AI Vanheim was massing serfs and other cheap troops
HoneyBadger, your tests do not prove anything because the AI is not going to play as though it were using a bless strategy.
A few nations are overpowered... it happens in a game this vast. Will it get fixed? Who knows, but I imagine if it does not, players in multiplayer games will regulate it by choosing bless nations in blitzes to fight (insert uberbless here) or several players will gang up on the bless nation in larger games, hopefully before the nation is allowed to expand too much.
I think you can determine if a nation/strategy combination is overpowered by holding it up to the following test...
If you have no concern about what your enemies are doing, and are able to focus on YOUR strategy, then the nation may be overpowered.
If you have to completely adapt your nation to stand a chance against a certain enemy, then the enemy nation is probably overpowered.
From my limited experience in multiplayer, it seems that the idea is to have a mixture of both, trying to work your strategy and trying to adapt to enemy strategies. If you place an overpowered nation into the mix, that goes out the window, and your either the overpowered nation massing a troop, or the balanced/underpowered nation trying to work a strategy to survive.