Theres isn't really much to do in the overworld of OoT and MM either, is rather dig for treasure in predetermined spots or do battle with your arrows. Boulders and holes are the same as the light treasures have at sea, and they sure picked my interest more than once, there were also pirates outposts, submarines and plenty of enemies. The ocean also had puzzles, and I personally liked the naval combat of the game. Although Im sure there will be neat locations, because the wind waker also had them, a 45 min long overworld is pretty much the same as an endless green ocean unless is filled from top to bottom with stuff, and not just boulders and holes. The ocean as a setting actually offers a lot of possibilities as well, but unfortunately the Wind Waker was rushed, otherwise the overworld of the game would be much more filled.
And this is something that makes me think, because even though the game was rushed, I wouldn't say the ocean was "filled with nothingness" as you say, it had a lot of treasures, locations and secrets, and still it seemed a barren world, mainly because of its huge size, so its not crazy to think TP might be the same when they are promising the overworld is even larger.
Its not the setting what matters, is the dedication put into it, be it ocean or land. Both locations have the same potential. For now we can only speculate, but I have the hunch that even if TP overworld is as scarce in content as the WW one, people would love one while still hate the other because the gaming community really is that lame.