A bit more on the principle of harmony:
67. The best instance of harmony between the Old and New Testament readings occurs when it is one that Scripture itself suggests. This is the case when the doctrine and events recounted in texts of the New Testament bear a more or less explicit relationship to the doctrine and events of the Old Testament. The present Order of Readings selects Old Testament texts mainly because of their correlation with New Testament texts read in the same Mass, and particularly with the Gospel text.
Harmony of another kind exists between texts of the readings for each Mass during Advent, Lent, and Easter, the seasons that have a distinctive importance or character.
In contrast, the Sundays in Ordinary Time do not have a distinctive character. Thus the text of both the apostolic and Gospel readings are arranged in order of semicontinuous reading, whereas the Old Testament reading is harmonized with the Gospel.
68. The decision was made not to extend to Sundays the arrangement suited to the liturgical seasons mentioned, that is, not to have an organic harmony of themes devised with a view to facilitating homiletic instruction. Such an arrangement would be in conflict with the genuine conception of liturgical celebration, which is always the celebration of the mystery of Christ and which by its own tradition makes use of the word of God not only at the prompting of logical or extrinsic concerns but spurred by the desire to proclaim the Gospel and to lead those who believe to the fullness of truth.
This last point could be debated, I suppose. In a way, the broad sections of the Gospels do have their themes: the moral sayings in Luke, the Sermon on the Mount or narratives of the Reign of God in Matthew, certainly the Bread of Life Sundays inserted in the Year of Mark.
What do you think: would Ordinary Time serve the people of God better if it were organized for the benefit of explicit homiletic themes?