Let's keep calm here...
Luna: Not only would she be helpless handling the moon (or sun if she has to fill in for an ailing or injured Celestia), but she would furthermore not be able to dreamwalk (and would have all the tact of a hydra when dealing with the traumatized).
Celestia: Could do nothing with the sun.
Maud: Would not be able to tell granite from gem-quality tanzanite from concrete.
You wouldn’t want Chief trying to help if your house caught fire.
Aramau: Would make ME look organized and tidy by comparison.