Airburst rounds existed in WW1 too. The point is, you hide in a bunker until the shelling is over, then you come up and man positions before the enemy can reach your trenches, or failing that, counterattack while they are cut off from supplies and reinforcements.
Airburst rounds with timers set by calculation, not airburst rounds that can blow up when they reach a specific point determined by proximity, distance, GPS, etc. It's a completely different kind of airburst.
