The Great and Powerful Trixie: Arrogant pony who wanted to prove she’s the best by causing humiliation to other ponies with illusions and deception.
Lightning Dust: Arrogant pony who wanted to prove she’s the best by causing humiliation to other ponies by recklessness and aggression.
Fanon that is/will be developed for both: Young filly who wanted to be the best, so she trained for so long through many hardships and developed a arrogant personality. With one fell swoop of an episode, she is shown up by the main character and leaves broken and miserable like she was before.
As everyone else has said, one mistake yes, but a mistake that you caused which risked not only the lives of your fellow Wonderbolts-to-be but also those of five innocent civilians.
Trixie: made fun of ponies which inadvertently lead to slight property damage
Lightning Dust: directly endangered the lives of multiple ponies for her own success and was okay with manslaughter(ponyslaughter?)