All Spock has is the Jellyfish. How do you know he can even defeat Nero head to head? How do you know that the timeline might not get screwed up even more? Anyway, your time travel argument is moot because that idea can be applied to ANY instance in Trek when a disaster happens. Why not just go back in time and fix it? The fact that you are using that point to try and rip this film, but choose to ignore all the other times in Trek that the time travel plot device can be used completely destroys your argument.