The problem is Skyla is both right and wrong with her air battle prediction against Ash.
If Ash kept his current team of 3 when the battle started, Skyla would have won that battle.
However, what she ignored was the fact that Pikachu vs Swanna would be a W for Ash and the other 2 battles would have been a loss for Ash. Skyla was only calculating it via one-on-one battles and count up score that way type-wise (or in the case of Tranquill vs Unfezant, one is fulled evolved over the other so it's easy to say that Unfezant has the advantage).
She never once considered what would happen if Pikachu single-handled defended ALL 3 of Skyla's Pokemon as per an actual Gym Battle. After all, they are all Flying-types and Pikachu is Electric. By that metric, Ash should win the Gym Battle.
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