Post History

One way to model the role of structure in storytelling is to think of "layers". For example, at some very-high-detail layers (which I would call the lowest layers) a story is made up of a sequence of words, or (even more detailed) letters. Obviously, using the same old 26 letters over and over again doesn't make your story good or bad, it's just your infrastructure. Some higher up layers (less detailed) get more interesting, but they still don't explain what makes a good story, e.g. good sentence structure vs. incomprehensible sentence structure: you still need good sentence structure, but you (probably) won't tell good stories if you care about nothing but sentence structure.
The previous examples were unrelated to storytelling, and so were extreme examples. Once you get to issues that do relate, specifically, to stories, the distinctions are less obvious, but the layering is still there. By the way, there isn't going to be a single, correct way to identify such layers, but there will always be ways to organise ideas into groups so that they relate to eachother in structured ways. For instance, I might define a lowest level of storytelling structure by identifying resources--your story will (probably) involve characters, locations, plot events, etc. We haven't brought these into relation with eachother, but that doesn't mean this layer only exists before you write or read the story: this layer is always there, it's the simple collection of the basic components of the story. Let's say the next layer is small-scale storytelling patterns such as the juxtaposition of character attributes like competence and sympathy, try-fail cycles, etc. And the next layer is entire-story-scale storytelling patterns such as the three act structure or hero's journey. What are you doing? You are starting from simpler materials and combining them to build more complicated and effective structures (like letters -> words -> sentences). You will often explain the qualities you want in one layer in terms of the lower layer whose elements are your building blocks, e.g. when you talk about economy of characters, you might say that if a character already existing in your lowest level (pool of resources) can fill a certain role in a storytelling pattern, use that character, rather than inventing a new one.
Now, your search for meaning and purpose in storytelling is fair. Your point can be expressed like this: using well-understood, traditional materials to build a new story isn't good enough; you still care about *what* you are building. There is a layer higher than all the layers mentioned so far, where we care about *meaning*, about *vision* as Mark Baker said in his answer. So your three act structure or hero's journey are *tools* and the question is: what are you using these tools to do? Just as incomprehensible sentence structure will make a story unreadable no matter how well you did in every other layer, so also incompetence in "storytelling craft" might derail your "vision", obscure your "meaning" (again, good structure is "necessary but not sufficient"). And just as beautiful vocabulary and intricate sentences will not make a good story, so also good play with storytelling structure can fail to produce a story that has any real reason to exist.
What *does* make a good story? That's obviously a tough question and I won't attempt to tackle it. But it will usually need to be competently built, from the grammar to the plot structure, and then you also need that extra magical sauce of having something important to talk about, or something funny, and so on.
An interesting final point is to consider what flaws in your tools will make the final construct less successful. There are actual mistakes: you can simply get your grammar wrong, however serious a problem (or not so much) that might be in each specific case. But in the higher layers, such as storytelling patterns, readers do start having a rather interesting response based on their familiarity with what you're doing: if the way you use your tools is too familiar, they detect a trope, and may dislike your story, but if what you do is too *unfamiliar* they may also dislike your story, finding it too strange, or confusing. And so, we have this endless hunt for interesting story structure, where we (often) want to use the historically successful tools, but also add just enough twists to keep things interesting. Nobody said mastering storytelling structure would be easy. *But* this still does not in any way equate storytelling structure with "meaning" or "vision", that other layer even higher up in the model is still there and still poses its own challenges.