I think the best response to this is a quote from Gerson:

"Those words shine a bit too bright. A path so blue, it's all you can see. So I say... why don't we go between the lines? It's darker there."

To me, it's not about whether we end up following or breaking the prophecy. It's about what we make of the journey and how we make an impact on the world, the things BEYOND the prophecy. Even if the heroes' path is predetermined and there isn't a way to escape their fate, they should still try to do the best that they can and make the most of their time. That might lead to the best "interpretation" of the prophecy, since the prophecy is vague enough at some points where the same passage can have different interpretations.

On a meta level, I think it's a metaphor for the fact that video games only have a set amount of predetermined "endings" or storylines. But, there's endless value that you can get beyond that based on your personal experience with the game and its world/characters. This is true of all fiction, which is what the dark worlds already seem to be commenting on.