From what we know in the actual chapters before the routes began, Nariyuki only took the hand of one girl. But the final chapter has him touching all of them instead.
This means the final chapter is actually an alternate universe, and only the stories of routes 1-5 are truly valid with what we know of in the canon of the story. Basically, route 6/5 is an alternate universe, meant to only hammer home the idea that the future is limitless, and that any route is possible. So at the end, when the girls saw glimpses of their routes, it doesn't mean that those were just dreams, but glimpses of something that occurred in another timeline. Route 6/5 is an open future, as him touching all the girls and the fact that the legend was just a story anyways, means that anything is possible for their futures as long as they believe in it.
The myth being made up hammers home the point about the author's message against fate; the girls aren't meant to study what they're good at, but rather what they actually want to do. And the people who believe in whatever future they choose are the ones who can achieve it in the end. This also fits with the idea that any one of routes 1-5 is canon, depending on what the reader believes in.
But this doesn't inactivate the progress in routes 1-5 or make them just imaginary, because those are the only routes that fit with what we know in the story. Route 6/5 is just an alternate timeline meant to strengthen the author's point.