Too Many Advantages.

Not many are using the air-based fortresses since they are more expensive and will be the first target of the invaders. But Legion used them.

The Tree Father had made many death stars as a Celestial. They have since been upgraded, so they cannot be wasted. Unlike the pyramids he built when he was a Celestial, which have long been destroyed, the death stars can be summoned by him. And they will have the power of Supreme Origin gods because they are an extension of him. 

The clones summoned the death stars around each of them and above the defensive shell. These preparations, combined with the fact that the clones are scattered throughout the divine plane, ensure that they will not be eliminated at once. This way, they will always be able to regenerate, resurrect, and summon whatever they lost and get back into the thick of battle.