Changes were certainly well underway before the Holy Week change. Permissions for the vernacular were being given more and more through the 1900s, particularly in mission territories. Then there was the “Novus Ordo” of the Breviary by Pius X, who really gutted the Roman Office. I’m not sure why he gets off scot-free when Paul VI gets his due criticism.
Msgr Pope is right that the Mass of 1965 was a much less jarring change than that of 1970. Though perhaps the modernists would have perverted any Missal they were given.
Pope St. Pius X? Perhaps you meant Pius XII. Changing the Breviary is a minor thing compared to the gutting of the Mass.
And then there’s the “minor” problem of Pope St. Pius V Quo Primum -”We order and enjoin that nothing must be added to Our recently published Missal, nothing omitted from it, nor anything whatsoever be changed within it.” But then again, that piece of paper was written long ago and could not have foreseen the changes that have come about. Sound familiar?