It would be a huge display of ignorance to abandon books written by theologians and religious scholars because they were written before the Second Vatican Council (Vatican II).
Vatican II no doubt brought about one of the biggest reforms in the history of the Catholic Church as a lot of changes were made to the customs and principles of the Church. However, you would not rule out the fact that the Council’s documents were built with references to ancient and medieval writings including the Bible. This is because one cannot tackle problems of the present without making references to the past occurrences of similar nature.
For everything that happens in the present, there’s always a link or connection to the past. So, leaving out pre-Vatican II books and reading only post-Vatican II books would be a loss of great knowledge as knowledge of the past is knowledge of the future.
In George Santayana’s words, “Those who cannot remember the past are condemned to repeat it.” The importance of books written before Vatican II cannot be overemphasized as they formed the basis for every other book written after Vatican II.