Well, work boats can only be built in coastal cities, so if that were the case then coastal cities would have stronger lakes than inland cities, which doesn't really make sense. The current system is more or less balanced, I don't see a reason for a change.
Ah OK. But it can use workers then, same as in case of Indonesian Campongs. I don't like that Fishery improves only 1 resource, and this building comes not very early.