Athanasius lifelong “obsession” was to insist Mary was the mediator between Creator and Creature was he wrong about this and right about all else? Lots of Saints agree.
Rereading the thread, this (emphasized) jumped out at me.
It is incorrect.
Saint Athanasius is noted for defending the divinity of Jesus Christ over against Arianism, in other words he was dedicated to an orthodox conception of the Holy Trinity. It is for this reason he was banished more than once. He suffered greatly on this point.
One of the arguments used by his opponents, those who thought Jesus was a creature but not also divine, was to disparage His mother (being as she was, something like a single mother in the thought of the day, the Jews and Arians both used that tactic to show Jesus could not be God due to impure origins). For this reason, orthodox believers would rally to defense of her reputation, and magnify her. This is the context in which prayers of this type began to be written during the lifetime of Arius.
As to the prayer quoted here. It does not support the point you seem to be trying to make. Being granted all grace was as a recipient. The noble saint is appealing to her goodness, hoping for prayers from her.
We all receive some grace, undeserving and helpless as we are it is always given to us, we never can just ‘take’ grace or ‘give’ grace, it is not a commodity for storing, we can’t parcel it out. We act on the Grace of God. It is through the Grace of God that we can do anything, even pray for one another. This is how grace is mediated, we act upon it. Grace is used as a verb, not a noun. Saint Mary of Nazareth was indeed ‘highly favored’ in this regard, in appealing to this great goodness in her the saint seeks her prayers, not a parcel.
Grace is God.
"First of all, then, I ask that supplications, prayers, petitions, and thanksgivings be offered for everyone, for kings and for all in authority, that we may lead a quiet and tranquil life in all devotion and dignity. This is good and pleasing to God our savior, who wills everyone to be saved and to come to knowledge of the truth.
For there is one God. There is also one mediator between God and the human race, Christ Jesus, himself human, who gave himself as ransom for all. This was the testimony at the proper time. "
Paul, an apostle of Christ Jesus 1 Tim 2 1:6
" …we do not cease praying for you and asking that you may be filled with the knowledge of His will through all spiritual wisdom and understanding to live in a manner worthy of the Lord, so as to be fully pleasing, in every good work bearing fruit and growing in the knowledge of God, strengthened with every power, in accord with His glorious might, for all endurance and patience, with joy giving thanks to the Father, who has made you fit to share in the inheritance of the holy ones in light.
He delivered us from the power of darkness and transferred us to the kingdom of his beloved Son, in whom we have redemption, the forgiveness of sins.
He is the image of the invisible God, the firstborn of all creation. For in Him were created all things in heaven and on earth, the visible and the invisible, whether thrones or dominions or principalities or powers; all things were created through him and for him.
He is before all things, and in him all things hold together. He is the head of the body, the church. He is the beginning, the firstborn from the dead, that in all things he himself might be preeminent.
For in him all the fullness was pleased to dwell, and through him to reconcile all things for him, making peace by the blood of his cross (through him), whether those on earth or those in heaven."
Paul, an apostle of Christ Jesus 1 Collosians 9:20
" … let no one boast about human beings, for everything belongs to you, Paul or Apollos or Cephas, or the world or life or death, or the present or the future: all belong to you, and you to Christ, and Christ to God."
Paul, called to be an apostle of Christ Jesus 1 Corinthians 3 21:23
The above three citations are quoted by the Old Catholic Encyclopedia under the heading of
Christ the Mediator.
A mediator is one who brings estranged parties to an amicable agreement. In New Testament theology the term invariably implies that the estranged beings are God and man, and it is appropriated to Christ, the One Mediator.
Lord have mercy. (Also, Copts tend to have less of an issue using what you might call “common terminology” for their specific ideas, as you can see in Fr. Tadros’ book, the heading for the relevant section I’ve quoted is “Our Mediatrix”! 
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Everyone has mere assertions, but you have facts, huh? Gee…why do the rest of us bother, then…