I never said they would be limited to certain moves, but Pokemon Trainer by standard is limited to 4 Pokemon moves. I just classified them by type.
If they were caught off guard or got confused this gives Torterra time to move first. This, the reason why earthquake is used.
If we had Rapidash out first, fire would be ineffective, however, Rapidash also can’t do anything unless it has a psychic type move, or in the recent remade Diamond and Pearl games, it learns Smart Strike upon evolving into Rapidash.
Floaztel solves the fire issue and so does Garchomp.