First off, general cats don't hate water. There are several breeds that are known to go fishing and/or hunt waterfowl, and individual cats from every breed that can be quite cheerful about the prospect of a hot bath. What the cat hates is being in an environment they aren't familiar with, which is not an incomprehensible attitude, I think.

The ships' cats I've met were, to a kitten, born on a boat, or in a shipyard. They grew up on boats, either on the sea or in dock, and when on land, rarely venture further inland than the shipyard or the inland side of the dock. They're not familiar with land, they don't like it, and they much prefer planks (or these days, fibreglass) beneath their paws, thanks.

I don't doubt that some kittens that were born to the cats that came on the boats stayed in Greece. But I would expect that the vast majority of kittens (that survived - ships' cats worked and there was no extra food for a furry soul) were traded between ships' crews (to older ships to replace cats that had died, or to new crews that didn't have a ship's cat yet) and stayed at sea.

So I think your equation is flawed from the beginning, because the kittens just wouldn't leave the ships.