I think that's going in the wrong direction. I don't want to re-hash a recent conversation from another thread, but I think being able to spam mines on every hill is a mistake. Others disagree and think it's important to be able to improve every tile with early techs, and they would likely agree with your suggestion about fishing boats for the same reason. Me, I think even being able to put farms on every flatland is a mistake.
Nope, I certainly do not agree with the suggestion to add fishing boats to every tile. The thing with coast tiles is that they're
fundamentally different from land tiles, in that, y'know, it's water. And that adds a fantastic opportunity for diversity: While land tiles get improved, sea tiles
don't, but instead coastal cities get different advantages, like producing more gold (kinda underrepresented in Civ VI imo) and of course having harbors and therefore being able to build navies.
Regarding mines, nerfing them would be fine to me. Removing them is removing a core element of this game, namely that you can improve all (fertile) land tiles. Another option would be to add new improvements, like Civ IV did with windmills, watermills and workshops. I got quite a few ideas for that, actually, so if you got any modding experience let me know.
Being a Kiwi I have the right to say that Auckland is not a very productive place.
I couldn't say anything about that, it's literally the other end of the world. What I meant to say though, is that, in my opinion, having a city state that adds production to coastal tiles is good, but having it by default is bad.