In Mass Exodus by Stephen Bullivant, several studies in America and Great Britian show that Catholic retention of its followers was higher other than religious group in the post Vatican II era. It was better than Lutherans, Anglicans, Pentecostals and many others. The book does an excellent statistical study of the reason why people left and when. Stephen notes that “Let us be clear here. Even had there been no Council, no deep and rapid liturgical reforms ….. Catholicism would have had a fairly torrid time of the past half century. As has been shown, ‘leakage’ was already a recognized and worried about .. in the 1940s and 1950s.” He details how Humanae Vitae (which alone may have caused most to leave) rocked the boat, urbanization rocked the boat, the sexual revolution, clerical abuse (which alone may have caused most to leave), and several other large scale non-Vatican II problems made many people leave. In fact, he claims that the Church Fathers at Vatican II should have done better because several already knew and had done studies to show that people were leaving the faith. As a result, he claims that Vatican II along with other secular trends (not one or the other) is to blame for not retaining more people.
On the other hand others do not blame Vatican II because the history of the last 50 years is so complex it really is hard to say what Vatican II’s role really was.
“But it is not quite clear that Vatican II failed because it did not stem the tide of disaffiliation. It is more likely that the Council fathers did not even perceive the scope of disaffiliation on the horizon, the social changes that were to sweep Europe and the United States. And it is possible—although sociologically impossible to prove—that it is the post-conciliar church alone that will have the resources to respond to the real crisis, the one that the Council fathers could not have recognized.” Review: Why did so many Catholics leave after Vatican II? | America Magazine
The graphs below show that Africa had an increase in Catholic but also Christian population since Vatican II. Yet, because other Christian groups increased it could not just be because of Vatican II. What we can say though is that Vatican II did not stop the increase!! (So maybe it did not cause the decrease in the west???)
Vatican II with Paul VI did allow for the Church to develop non-Italian European leaders. It has only been post Vatican II were we can truly say the church leadership represents all peoples. This is one of Vatican II fruits. Before Vatican II, the majority of Popes, the majority of cardinals were all Italian. Vatican II paved the way for this to change.
“The Word on Fire Vatican II Collection” from Bishop Barron – Major Fruit of Vatican II -the Role of the Laity. How many lay associations can you name or have impacted the Church! Opus Dei is a lay group! Communion and Liberation is a lay group! the list is long.
More Scripture! Fruit of Vatican II. Vatican II greatly increased the diversity of scripture read during mass compared to the old rites. Did the pre-Vatican II Mass really have more Scripture than now? – PrayTellBlog (Plus Dei Verbum has some excellent teaching on Divine authorship that have deeply influenced and clarified Scriptural theology)