If there are alot of water provinces that form a big continous ocean then a double bless is well worth it as EA Oceania.
As you can slaughter the other 2 water nations and use voice of tiamat to give you a huge gem income very fast.
Once you are the only water nation, leave the land nations to fight it out well clamming and fever fetishing like a mad fish from hell. Then pump out loads of seraphs and other high level summons and wipe out the remaining land nations.
Seen it done a few times...
But EA Oceania is overall balanced, as its also failed alot of times as well.
I personally have fought Ea Oceania and Ea R'lyeh (in 2 different games) as Ea Atlantis. I could not defeat either but I managed to fight them to a stalemate. All nations involved were played by good players, its tough but possible for the other water nations to survive.
In one I made good use of the basalt kings/queens as good thugs vs Ea R'lyeh and in the other vs blessed knights of the deep, I had to use my mages (lots of mages) to mass spam school of sharks to keep them occupied, water elementals to kill them and destruction to get rid of there protection.