I do miss how Civ5's maritime buildings gave production to sea resources. I was a bit disappointed there is only 1 food and 2 gold for sea resources in the harbor in Civ6; while I really love the shipyard's mechanic, I could see how the fact that we lost the extra fishing boat hammer was hard on our coastal cities. I think if one were to add that, though, it best be applied to fishing boats and not just sea resources generally. That's only 2-3 production in a decent coastal city, but it would make the fishing boats feel more substantial. (While leaving coast tiles where they are.)