People in the current world had not realized the importance of air superiority, not because they lacked intelligence, but because of the world's stage of development.
The current world resembled the Middle Ages. Most places were still in an era of competing for land power, while only a few places had begun tentatively vying for sea power. As for air power... no one had thought it could be of any use.
Take Modern Earth during World War II. Before aircraft carriers gained unimaginable advantages over battlecruisers, no one thought air superiority would be so important. Yet in an extremely short time, the way wars were fought changed completely.
That said, just because no one had thought of its use did not mean it was truly useless. It had merely been used in a distorted way.
Take battles between Wizards as an example.
At the Level 1 Wizard stage, battles between Wizards mostly took place on the ground. On one hand, Wizards' abilities were relatively limited, and remaining airborne for long periods consumed too much energy. On the other hand, they could easily be focused down in the air and had difficulty dodging, whereas this problem did not exist on the ground.
At the Level 2 Wizard stage, aerial combat became quite common, because the many obstacles on land had begun to impose varying degrees of restrictions on a Wizard's strength. Only in the air could Level 2 Wizards gain better visibility and unleash their power more effectively.
But this kind of battle was not a struggle for air superiority. It was merely an extension of the struggle for land supremacy.
When most Wizards fought while floating in the air, they generally stayed no more than a hundred meters above the ground. They also stopped making large-scale movements once airborne. Like