LongStrider
Wow Did the discussions go wild on this one. Well Thread necromancy! Here’s a different explanation, based on something someone wrote in a fanfiction that actually explains this perfectly. Twilight didn’t lose a contest of speed; she lost a contest of preparation. We know Starlight was leading them into a trap. She was planning to unmark them from the start, and they unintentionally gave her the perfect opportunity. So, she had a plan. Basically, what happened was that, when Starlight picked up the staff of sameness, she actually began gathering her strength and preparing her spell to fire. Her speech partially done to keep up her act, was really just a way to stall for time. Notice how she seems to drag the conversation and act kind of theatrical with the staff. She was buying time to get her spell ready. Also, when her minions came in, it further distracted Twilight who began to panic. When Twilight figured it out, it was too late!
Starlight had her right where she wanted her. Unprepared, panicked and distracted. While Twilight thought of the whole room, Starlight focused on only her. Thus, before Twilight could even begin gathering her power to do anything, Starlight had her spell ready to fire. Twilight was doomed before she could even try, and she and the others lost their cutie marks as a result.
Starlight had her right where she wanted her. Unprepared, panicked and distracted. While Twilight thought of the whole room, Starlight focused on only her. Thus, before Twilight could even begin gathering her power to do anything, Starlight had her spell ready to fire. Twilight was doomed before she could even try, and she and the others lost their cutie marks as a result.