This doesn't seem right. if your lucky and do it right, you can have a city completely surrounded by a fresh water lake and, combined with OO, your pretty much invincible.
And its unthinkable that the ability to cove is fine with many players? Even if you can make lots of freshwater (completely surrounding it in freshwater is impsossible since if you make the lake to big it turns ocean. You'll usually have 3 different lakes divided by land-bridges in a former non-costal city with one acess to ocean.)
+ Lanun are supposed to be strong near water and OO is their strongest religious synergy so it ought to be the best combination possible for them (like Elves and FoL with lots of forests around or Dwarves with RoK and alot of hills around are.).
Add to that only 4 Ports at max per cities (one usually ocean with connection to a large body of Water for many reasons beeing better than all freshwater) / 2 or 3 beeing standart and easy destructability + compare the whole thing to elves (yes they are powerful as well but still balanced as outlined by the teams take on balance.) with forest-cottages or forest farms and one can't speak of this beeing the best or earliest economic option in the game (in fact several civs have better economic options than 4food + 2 or 3 commerce including any civ via farms with agriculture + aristocracy + sanitation. Especially Financial leaders which yield 4 Food / 4 commerce next to a river and 4 Food / 3 Commerce without a river . With ports beeing comparable to resources but destroyable unlike those) + consider the extreme cost in used workers to accomplish cities with lots of freshwater and its not anymore all that hot. Tactically its still very nice but requires heavy investment of workers to use tactically on large scale.
What is so hard abbout accepting things that are powerful as they are without changing them because you! don't like them?
The same complaints about terraforming come up again and again. FFH2 is all the more fun with terraforming imo (including coves). And im not the only one to think so.
If you hate terraforming so much, either chose another mod or modmod it out (or have someone modmod it out for you.

). Both very solid options to accomplish what you want.
Its not like you are forced to play unmodded ffh2.
(And if multiplayer is the main reason for your complaint: Its not the main focus of FFH2 Design. Not completely unimportant though.)
If you complain because AI can't really cope with that strategy up until now wait until the AI is updated and gets a grip on the naval part of the game. Rest assured the team will get that done. (It was done in vanilla Civ as well so this one is doable for sure.)