The function of all muscles depends upon the relative positions of the bones that they control. Most anatomy references analyse muscle movement from standard anatomical position, and hence fail document the full breadth of movement that some muscles can affect. And this is particularly true of the shoulder girdle, since it is comprised of a shallow ball-and-socket joint, which itself is translatable through movement of the whole joint structure. The pectoralis major, for example, is exemplary in this regard because it can adduct, flex and extend, and medially rotate the humerus, but also depress and protract the whole shoulder girdle.
Thus, a single muscle can be dominant in numerous distinct or opposing movements—hence the apparent paradox of the pectoralis major's performing both pushing and pulling.
The complexity of the body's musculature is such that distinct muscles, muscle heads, and even the muscle fascicles within different regions of a penniform muscle work most efficiently through certain ranges of motion. Indeed, the very reason that the body contains such a large amount of apparent redundancy is that it is designed to handle complex movement through a vast range of angles and positions efficiently.
Hence, the regions or fibres of the pectoralis major that are dominant (and therefore most heavily loaded and stressed) in a pull-over are different from those which are dominant in a bench press, dip, fly, or other movement. And this is why one of the fundamental principles of hypertrophy is to employ a large variety of exercises, and variations on those exercises.
Without such variety and variation, our muscles are more specialised, but consequently less balanced and defined. That is, we develop size and strength for a particular purpose, but not for a broad range of purposes.
So whilst the pull-over and other pulling movements certainly do involve the pectoralis major, they will not develop it well for pushing movements. And the size and shape of the pectoralis major will reflect that difference.
I hope that answers your question.