If you read the article again, it identifies the word “mystic” with those people who suffer this absense of God or Dark Night of their soul.
I do appreciate your interpretation of the word, but I do not think it is the only definition.
IMHO, God the Father withdrew from the Christ so He could suffer the pains of all, including loneliness and a feeling of abandoment, among others I am sure...so He could carry our sins, and our hurt, and redeem them and atone for them perfectly.
I have no doubts that in principle, God from time to time does the same for us, so our faith can be purified, even as He was made pure.
Did that happen to Mother Tereasa? Could well have...it is between her and her Maker. I do know this...her fruit bears testimony to her continued faith, depsite whatever hardships.
Does the etymology correspond to the word “Mystery” as in “Mystery Church Age”. That word for mystery derived from the Greek MUSTERION, for hidden.