Yes, if no city has enough fish/lakes to justify building Moai earlier, putting it in a junk city is often better than not building it.
How many is that (ballpark)? How is that number affected by modifiers (stone, OR, forge, etc.)?
The map will often contain many marginal situations; a strong seafood location on an island might make for a very quick 2 pop whip build with MS; but such a location might be better served as a NE city. Likewise a cap with a few lakes and seafood might make for a strong MS location, but with enoughYou guys can yammer all you want about what's better in principle, but the map will usually tell you what you need to do. This is just such a case.
