Thank you for explaining, now it makes sense!
I applaud your effort to educate SSPX priests on this dangerous deception.
I believe the best way to kill the devotion is to expose Faustina, her pride and heresies so I encourage you to recommend them MHFM's video as well.
I think you should watch the middle part on the timeline of the development of the devotion.
New Devotions were banned in 1937. I believe Fr. Sopocko is the originator of the devotion, not Faustina. He was writing theological papers on the need for a feast of divine mercy, but he kept getting denied by Bishops and even the Vatican. I believe he wrote the Novena and Chaplet (which borrows from a previously condemned Chaplet of Mercy).
He realized he would need a supernatural revelation to win over the Bishops and Church to approve a Feast of Divine Mercy despite the ban.
Since this video, with the new research, I am being led to believe no nun named Faustina wrote a complete diary in the 1930s. I believe it was starting to be cobbled together by the religious order Fr. Sopocko created during WW2.Fr. Sopocko was working for the Polish military intelligence service in WW2, his female religious order was as well - part of the polish resistance. There are so many heresies because it was written by young women with no Catholic religious training (like a 33 year old nun would of had if she had joined a convent in 1924 and died in 1938) or perhaps weren't even catholic, but Mariavites.
From my experience, Novus Ordos don't really care about heresy, and certainly won't listen to SSPXers or sedevacantists accuse it of heresy because we are "schismatic". They are emotionally attached to the myth of Faustina, because of all the emotional propaganda that has been used on them by the word "Mercy". So they feel they are showing mercy to faustina by defending her reputation which the don't even know. Afterall you attacking a poor, barely educated nun who could hardly read and write, its mean, it's bullying and unfair in their mind. They don't really care what's in the diary, for them its about the chaplet.
Go after the chaplet. Go after the people who promoted the devotion to show that they were not inspired by an uneducated nun's visions to promote the devotion, it inspired disobedience to the Church hierarchy. Expose the lies in the narrative. The narrative being a lie doesn't have the protection of the the Vatican 2 approval.
The excessive pride in Faustina's diary is due to Polish messianism and most likely written by someone who was a Mariavite or well acquainted with them. The Mariavites had female priests and gave communion under both species. When you understand this, then you understand why the diary contains so many references to her holding the host in her hand, standing on the altar dispensing graces, holding sacred vessels and receiving communion under both species.