[Meglobob]

I think that since EA Helheim got its nerfs, there is now no single outstanding powerful nation.

Indeed the only balance problem that really exists with any of the nations over the 3 eras is one of being too weak compared to some of its rivals in that particular age. This applies to 2-3 nations only.

There is now a whole bunch of nations who are powerful but really only have a slight edge on other nations.

LA - Ermor/Rlyeh probably have a slight edge.
MA - Probably the most balanced, only Pythium stands out as having a slight edge.
EA - Oceania (if there are alot of water provinces), Lanka, Caelum, Niefelheim.

I think the map/player/diplomacy/site % all have a bigger effect on the game than individual nation choices.

Just look at perpetuality, it was so influenced by the inbalance of water provinces to land provinces.