Pope Francis is talking out of the back of his head: St Pius V said the same thing in 'Quo Primum' but Paul VI overruled him.
The question is, whose Magisterium do we accept; the latest one?
Liturgical reforms since Trent have never altered the structure of worship until Vatican II.
Another Pope or Council can quite easily undo the 'reforms' of Vatican II just as easily as Vatican II undid Quo Primum.