The W3C answer to this is a strong "yes". They consistently advocate separation of semantic and presentation concerns, and if that is done rigorously, then unstyled HTML should make visual sense, because the default behaviors for paragraphs, definition lists, captions etc. are designed to make visual sense. The point is not so much that people will have stylesheets turned off (except when we're talking about accessibility); it's that this will work as a side effect of coding "correctly", and so can be used as test of markup quality.
But that answer is so unrealistic it's nearly worthless. Almost no one uses purely semantic tags like
colgroup, let alone the newer HTML5 tags; and even simple text pages can't always be structured perfectly with just
Still, it's not a bad idea to be aware of how your page looks without CSS. In particular, if the order of elements is scrambled, that's a sign that your markup is a mess, which can make code harder to maintain and debug. And if you are making a list or a table, there's no reason not to use the right markup.