Karl Thienes points out that the role of intercessor to the King did not originate with Mary. (I must say I never thought of Bathsheba as a type of Mary before.)
Jennifer's comments include "the obvious Protestant question":
Why do I need to go through Mary to get to Jesus? Why not go directly to Jesus?
And the obvious answer -- "you ask your friends to pray for you, right? So why not the Mother of God?" -- is given.
It might help to make something implicit in that answer explicit: Those who ask Mary for her intercession don't "need" to do that to "get to" Jesus. We want to do that. We love and revere Mary; we have an active, personal relationship with her, just as we do with our natural mothers.
Asking, "Why do you need to pray to Mary?" is like asking, "Why do you need to call your mother every week?" It's not a matter of logical necessity, but of natural desire. It would be unnatural for someone who knows and loves Mary not to pray to her.