These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
The battle between Celestia and Nightmare Moon has now been shown in canon (as of the season 4 premiere), jossing the fic right from chapter 1.
Offscreen Moment of Awesome: Despite being the premise of the original short story, most of the Celestia vs Nightmare Moon battle occurs offpage between chapters 1 and 2. All we get to see is the conclusion, which is decidedly one-sided in Celestia's favour.