The Dogma of the assumption was not proclaimed until this century, for several reasons. There were numerous theological points to be discussed, points stemming back from over the whole history of Christian thought, and there were numerous scriptures to be taken into account. With so many factors to consider, and the Church being so extremely careful, and so desirous that all opinions be heard, the ordinary teaching of the Church, already received by so many faithful for many centuries, was not promulgated in an extraordinary way until this century.
Those who talk like this view suddenly appeared out of thin air in the 20th century are evidently ignorant of the doctrine's long and respectable history