Maybe in many ways their staves are used in a similar way as Sauron's ring, just not to such an extreme. Maybe they vested some of their power in the staff when it was created, so that when they have it, their power is even greater than before, but they are weaker without it. If their staves had no power, then Gandalf would have not needed it in Two Towers to save the King of Rohan.
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"Come away! Let the cowards keep this city!"
-- Fëanor to the Noldor
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