Well, the German operation in 1940 was a complete success, based on good training, planing and surprise. Nevertheless, th elosses were high.
Crete was the first attempt to attack an island out of the air without adequate naval power. Although the Germans reached their targets the losses were too high.
Allied airborne operation helped the landings on the European mainland. But again the losses were high. And you could not rely on these operations because the troops might land at the wrong place or just blown away.
Marketgarden was a desaster. Besides bad planing the airborne forces were just overrated.

Same happened at Dien Bien Phu. France lost 16.000 men during this operation against Vietcong.
Airborne units are very expensive. You selevct the best, give them best equipment and training. The effect is that very often these troops are overrated. And the losses are usually so high that it does not pay!