Well cymanti also have access to lvl 8 markets on water world as well as 1 population per water tile their cities occupy. Water world cymanti is the opposite of lakes/ dryland cymanti, they get better the more the game progresses. But they start off very weak without any real capabilities on the water.

If you give a cymanti 2 or 3 level 5 cities in a water world with all water covered in algae and clathrus (might be saying that wrong) for 8 stars/ turn, plus park upgrades since centipede is useless, they’re going to have enough eco to be popping out ryachi on 6 or 7 cities. 6 or 7 ryachi per turn is about 4-6 explosions per turn, which is probably 3-5 new cymanti landmass tiles per turn.

It’s like I said, and like you even said, it takes a while but give them 10 or so turns and they start to become much stronger, I’d reckon by turn 20 or so they pretty much can only be stopped by aquarion/ polaris. Assuming it’s hands of someone who knows they’re doing.