Um... 60% archipelago often ends up like a pangea with oceans in the middle. Or something kind of close to it. So it's possible everything ends up connected by coastal squares. Maybe as an overpowered example, in Moonsinger's 88k game (I think 60% archipelago) she had all the luxuries (most traded for, of course) by 10 AD and she hadn't learned Astronomy yet. Luxury potential on continents I think would thus work out as lower on average compared to both 60% pangea and 60% archipelago... because no doubt about half of the luxuries you simply can't get at by any means until Navigation or Magnetism, right?
Yes and no. You also can't get to luxuries that are way on the far side of the archipelago (even if connected), simply because it's too damn far to walk. Either way, you either have to go a long way to get them (by which time you probably have the capacity to sail somewhere if you need to, and it doesn't matter what shape the world is.
And okay, the luxuries don't solve ALL the happiness problems. But they solve quite a few. Markets are also a Very Very Very good thing, and probably worth researching ahead of anything in the bottom part of the tech tree at all. Possibly the second or third most important tech for a fast start (Republic #1 of course; after that it's arguable, but I think markets rank ahead of most everything else).