All of the “dubious” quotes provided are from people who the catholic church would consider to be doctors, saints or other reputable people in catholicism.
As I noted earlier this is the problem with catholic tradition. All of these guys could claim they received their authority from the apostles.
Much or what you say is true, but one must keep in mind that not every statement made by every reputable Catholic is in and of itself Sacred Tradition. That’s what prompted my question in post 256 regarding the statement by F.X. Durrwell about Mary as mediatrix of all graces. As for as I know, this has not been affirmed as Catholic doctrine, and, as such, is not Sacred Tradition.
The Second Vatican Council (Lumen gentium ## 61-62), said:
... in suffering with Him as He died on the cross, she cooperated in the work of the Savior, in an altogether singular way, by obedience, faith, hope, and burning love, to restore supernatural life to souls. As a result she is our Mother in the order of grace.
This motherhood of Mary in the economy of grace lasts without interruption, from the consent which she gave in faith at the annunciation, and which she unhesitatingly bore with under the cross, even to the perpetual consummation of all the elect. For after being assumed into heaven, she has not put aside this saving function, but by her manifold intercession, she continues to win the gifts of eternal salvation for us. By her motherly love, she takes care of the brothers of her Son who are still in pilgrimage and in dangers and difficulties, until they be led through to the happy fatherland. For this reason, the Blessed Virgin is invoked in the Church under the titles of Advocate, Auxiliatrix, Adiutrix, and Mediatrix. This however it to be so understood that it takes nothing away, or adds nothing to the dignity and efficacy of Christ the one Mediator. For no creature can ever be put on the same level with the Incarnate Word and Redeemer...."
We notice that Vatican II did not add the words "of all graces." However, as many papal texts point out, Mary's role in dispensation flows logically from her role in acquiring all graces. Further, the Council itself added a note on the above passage, in which it refers us to the texts of Leo XIII, Adiutricem populi, St. Pius X, Ad diem illum, Pius XI, Miserentissimus Redemptor, and Pius XII, Radiomessage to Fatima.
Leo XIII, in the text referred to, spoke of her, as we saw above, as having "practically limitless power." St. Pius X said she was the "dispensatrix of all the gifts, and is the "neck" connecting the Head of the Mystical Body to the Members. But all power flows through the neck. Pius XII said "Her kingdom is as vast as that of her Son and God, since nothing is excluded from her dominion." These and many other texts speak in varied ways of Mary as Mediatrix of all graces, so often that the teaching has become infallible. https://www.ewtn.com/faith/teachings/marya4.htm
And there's more if that's not enough.
Again, this is why Christianity rejects roman catholic "tradition" on this topic and many others.