FINAL FANTASY VII REMAKE INTERGRADE

The following strategy works on every opponent.

Equip the Grandmaster Board that you obtained by beating Chadley in easy/normal mode. Select the Guard Dog and Slug-Ray units that you own by default. The other 3 units you equip do not matter.

As soon as the match start, spawn a Guard Dog. Wait for it to make its way to the enemy outpost, then immediately spawn a Slug-Ray next to it. (If the guard dog isn't available at the start, just spawn the Slug-Ray first. The strategy otherwise stays the same.)

Keep spawning Guard Dogs and Slug-Rays as soon as they become available. If enemy units get in your way, use your thunder and aero spells to get rid of them. Thunder is especially good against barracks and facilities. If units are not an issue, use your thunder spell on the enemy Condor to remove half of its health. You may also use your stop spell on the enemy condor to prevent it from retaliating.

Doing this ensures victory before the enemy has the time to destroy your own condor.
The Guard Dog is used because it is fast, has high damage, and ignores enemy units. The Slug-Ray is used because it's one of the cheapest units in the game on top of being airborne, which means many grounded units cannot target it. Using the Grandmaster Board means at least one of the two is always available, and grants high ATB speed. The Assassin Board II may work as well.