I believe you are conflating dealing with your definition of "what a mediator is in court", and agreeing with your definition! What you fail to allow, Seth, is that mediation is not just a legal type of action, it is also relational! On the one hand the wrath of God is legally satisfied by the death of Christ; this is completed, and will never be repeated! It is finished! This is the Atonement!
But the relational factor between God and man still needs attention, and mediation is the means of this. As long as men feel the conviction of sin, as long as the message of the gospel to repent and believe is heard and the hearts of men seek for forgiveness mediation will be necessary! The man Jesus Christ is presently our mediator.
Doug