Replacement Theology is one of those things mostly named by those who oppose it. By some definitions, some Catholic teaching (and some of the New Testament) can be called “replacement” or “supersessionist.” By other definitions, including those that most easily fit what the Church currently and most durably teaches (and those in the New Testament), we should definitely not think of Catholicism as having a “Replacement Theology.”
Everything in this conversation lives between the declaration in Hebrews that the forms of sacrifice in the Mosaic Law had become obsolete now that Christ had become the perfect High Priest and perfect Lamb in one, on the one hand, and the declaration in Romans that God has by no means permanently forgotten Israel. In between these, we know that the Church organically grew from Jewish religious practice in the 2nd Temple period as it was transformed by Christ and sent out into whole world as it was then–and that in that context, the continuity between the People of God in the Old Covenant and the People of God in the New Covenant meant that the Church borrowed much from Israel, and spiritually identified the Promise entrusted to Israel with the Promise fulfilled in Christ–thus enjoying a status as inheritors of that Promise. You can therefore find statements all over about how “shadows” in Israel become “realities” in the Church, because that’s perfectly true. Whether you consider this spiritual interpretation of the history of Redemption to be “Replacement Theology” will then depend on your point of view.
If you consider any assertion that the sacrificial practice of Judaism at the time of Christ has been rendered obsolete by Christ’s perfecting of that sacrifice to be “Replacement Theology,” then the plain reading of the New Testament (especially Hebrews) is, too.
If you suspect, though, that this is an almost obtusely simplistic way to look at this teaching, especially in light of the larger conversation in Romans and Hebrews, then I think you’re right.
What is largely missed in all this discussion is whether the Church “replaces” Israel in that it now functions in the same manner and under the same economy as Israel–but surely we should say that the Church functions very differently than Israel (albeit with strong organic connections and profoundly meaningful parallels), and that the New Covenant is precisely a change in economy from the Old Covenant.
To use a very loose metaphor, God did not replace your old car titled in Maine with a new car titled in Maine; God said “I’ll take care of your car while you’re away” and deployed you to serve on an aircraft carrier.
It would be silly to say the carrier “replaced” your car, and sillier still to try to swim back to Maine in order to use that car to fulfill the aircraft carrier’s mission.
But the car, in God’s hands, may well still be functional, and may well be serving its own purpose. Your job is not to pester God about the car, but to serve Him on the aircraft carrier.
Does that help make sense of it?
Two more notes, then.
First, remember that the People of God in the Old Covenant and the People of God in the New Covenant are constituted not primarily as the recipients but as the conduit of Redemption–that is, we each receive salvation by means of the People of God, primarily by our attachment to that People (circumcision/baptism) from whom we receive the Promise and are engaged to proclaim it and participate in its fulfillment, and secondarily in whatever other ways God may choose to attach a Rahab or a Cornelius to Himself (even before they are able to be recognized as members of a visible communion). So that what has been “superseded” in the New Covenant is not the right of Israelites to receive the fulfillment of the Promise entrusted to Abraham, Isaac, Jacob, Moses, David, but the role of genetic Israel in proclaiming and fulfilling that Promise, and that only because “it worked”: Israel’s proclamation turns out to be the Word, Jesus Christ, and her fulfillment is in Him. (Again, if you call this “Replacement Theology,” then Jesus Himself taught His Apostles this theology. But I think that is a misnomer.)
Second, remember that there are many “theologies of” this or that among the faithful throughout history. You can find sainted theologians, very holy men indeed, who argued against the (mis)understanding common in their day of what have now been dogmatically defined as tenets of the Catholic faith. I am sure that Catholics have held to what can fairly be called “Replacement Theology” at some times and places. But what the Church has definitely carried forward as belonging to the deposit of faith, and what she now describes to us as the best understanding now available of the developing People of God, is not really a “Replacement Theology” in the sense usually intended.
Hope it helps.