Coast spots are not automatically good. Consider that an ocean tile is on par with a mountain or plain desert tile, and coasts are almost as bad. In almost all cases you'd rather work a specialist than a non-resource coast tile.
So, consider that a coast spot with 50% water has just removed your available city tiles down by half! This starts to put it into perspective.
The best coast spots have many resources and minimal (ideally ZERO) non-resource water tiles. Plus, the more resources, the better seaports are.
Is a city spot with 50% water or less, zero water resources, even worth it? Especially if it has a lot of hills and no river/lake, and few land resources? I suggest to avoid that spot... there are surely better places inland to put your cities.
So, this thread might be better if it asked, "What's better? An extra resource, or a coast spot with few non-resource water tiles?" Or similar.
ps also keeping in mind that a critical strategic resource, or 2 lux resources you don't have, is generally always a good spot regardless of coast or land.