It's not "meaningless". Yes, it's fiction, but it also has rules that have been well established by MANY prior Star Trek episodes and films. "Yesterday's Enterprise", "City on the Edge of Forever", "First Contact", "Trials and Tribble-ations", etc. etc. All deal with the time lines being broken (or potentially broken) and subsequently fixed.
Trek 2009 suddenly says, "forget all that, timelines can never be fixed, too bad." Um, really? Since when?
All fiction is made up, of course, and if you're venturing into the realm of sci-fi/fantasy and are creating fanciful concepts that don't exist, you darn well better at least have them be internally consistent otherwise nothing will feel like it matters and suspension of disbelief becomes impossible.