You can write JSON that exclusively uses strings, so this is not really relevant. Sure, maybe it can be considered an advantage that s-expressions force you to

You can write JSON that exclusively uses strings, so this is not really relevant. Sure, maybe it can be considered an advantage that s-expressions force you to do that, though it can also be seen just as easily as a disadvantage. It certainly hurts readability of the format, which is not a 0-cost thing. This is also why all Lisps use more than plain sexps to represent their code: having different syntax for different types helps.