The four of them are the beginning of the Faerie rainbow road of the Tetractys and they make a team. Without Dorothy's desire to return home they would never have attempted the journey and without the help of each one of them individually Dorothy could never have succeeded. Each played their necessary part. Similarly the witch of the North could not tell her about the power of the shoes. Her specialty was Purple, Location. She could tell her where to go. The information of what to do had to come from Glinda whose specialty was Red, Knowledge.

Oz being recursive means that things and people are where they are supposed to be. Kind of like the medieval notion that it proved that God was good because He caused rivers to occur next to cities. It occurs to me that the silver shoes might not only have the power to take you where you want to go but also the power to bring you what you want to have. Shoes as a symbol of travel and Silver as specific absence. Supposing the Wicked Witch of the East was afraid of the power of the great Oz, she might have brought the Kalidahs from their proper place in the distant North to a place on the Yellow Brick Road to act as a block between an army of Oz and herself. And perhaps been pleasantly surprised when the Land responded to their presence by putting a chasm all the way around them. In a recursive country dangerous things are far away or blocked off. Because of recursion there is no going around an impediment either. One can go back or solve the problem. Thus the Kalidahs would have made a very effective barrier to an army of the Great Oz. Then when the silver shoes were lost the spell was undone, the Kalidahs transported back to their proper place in the North and the chasm healed.