In all seriousness, why wouldn’t you just go with the Bible? No source of information is above the Word of God. None. There is nothing in the Bible that states you can pray for the dead (except that which is prohibited as wicked) and only Jesus Christ is our mediator with God, not his mother.
Again, did you read Gregory the Great’s interpretation in the aforementioned article? HE USES THE BIBLE, indeed the very words of Christ.