What did the Devil gain via Fatima? It led many people to return to God who had been led astray, and to this day is an inspiration to those seeking God (not the Devil).
He gained a stronghold in Mary worship.
The apparition insisted on a church built to Mary, and promises made about praying the rosary. That is not directing people to God.
And even if they are directed to God, that doesn’t mean they are saved. Scripture refers to those who have a form of Godliness but deny the power of it.
Jesus said that there would be many on that day who would say, Lord, Lord, didn’t we (fill in the blank) in your name, and He’s going to tell them to go away that He never knew them.
Getting people to Jesus is meaningful.
Getting people to *God*, not so much, especially if all it does is make them more religious instead of giving them new life in Christ.
Returning to ROME and it's 'Mary' is the same as returning to God?