Namaste. In Autobiography of a Yogi, Yoganandaji describes that the roles of Guru-disciple (i.e., Elijah-John and Elisha-Jesus) "became reversed" between their two separate appearances in time on earth. It seems that a reversal of roles like this can make sense if they were both Masters inwardly to begin with, and reversed roles only outwardly for earth’s drama? But what does this mean: "[Elijah] had given the "mantle" of his glory & his spiritual wealth to his disciple"? Did Elijah "lose" something/"realization"?
This is a question which I have pondered as well.
I have come to the conclusion that this "mantle" has more to do with an outer role than with inner realization. Yogananda’s writings on this point are not clear or consistent: his early magazine articles suggested a role reversal having to do with realization whereas later publications by his organization suggest otherwise.
Given that Yogananda — and, indeed, the world at large — consider Jesus to be what we would call an avatar (fully realized in prior lifetimes), it makes more sense that the "mantle" that was given him related more to the outward role.
This does, in fact, also accord with Yogananda’s statements about John’s humility, especially when he denied that he was Elias come again.
So the role reversal was indeed, I believe, an outward one for earth’s drama and the upliftment of humanity.