The thing is that humans have to take one step at a time. If we try to take more, we take none.
So the one step you proposed was an examination of "one mediator". But you didn't stay with it and raised the "summoning the dead" question. But when you try to do a little bit on each step you get nowhere on the entire argument.
IMHO the right way to proceed is to examine one issue at a time. First let's look at the one mediator issue until we have some resolution on it. THEN let's look at the "summoning the dead" issue. Your way of skipping from this issue to that guarantees no resolution of any kind, ever.
Mediate is WAY off and is a horrible misuse of language. If you think asking someone to pray for you is the same as "mediation"--especially when intercession is the term used earlier in the same passage--not mediation, then you're WAY off. To EVEN BRING UP, "If I ask you to pray for me" in a thread about MARY, it is YOU WHO BROUGHT SUMMONING THE DEAD INTO THE CONVERSATION--NOT ME.