It would be my thesis that systematic and exegetical theology are interconnected, yet separated disciplines. They are not identical with one another. Now, I realize that people who I respect a great deal (David Scaer would be one of them!) think that they actually should be identical. Nevertheless, I would argue otherwise. Here's why:
1. Exegesis deals with full historical meaning of a given text, systematic theology deals with the articles of the faith. Though infallible and inerrant, everything in the biblical text does not deal with the articles of the faith. They are related to the articles of the faith, but if certain aspects of them were different (for example the number of divisions of singers that David established in Chronicles), the articles of the faith would be no different.
2. According to the the dogmatic methodology that Melanchthon employs in the CA, what are the articles of the faith based on? Well, the sedes doctrinae, namely, the clear passages which gathered together mutually clarify one another and form the loci communes ("theological common places"). So, dogmatic theology deals with these. Now, this does not exclude insights from the exegesis of the total text from informing how we understand the loci communes. Nevertheless, dogmatic theology is primarily interested in the articles of the faith and not the overall historical meaning of a given book of the Bible.
3. This, I think, clarifies Ratzinger objection to the idea of the CA as a permanent symbol of the Church-catholic. What if better exegesis comes along? How does one mean this? The sedes doctrinae are perfectly clear and therefore better exegesis can't come along with regard to them. For example: "In the beginning, God created the heavens and the earth." What does that mean? Perhaps does it mean that in the beginning God created the heavens and the earth? Yes, of course! How does one improve on this? It's impossible.
Now, let's go to exegetical theology. If we go to exegetical theology, we will say is "well, of course we now understand that the text is rejecting certain cosmologies of the ANE and whereas in those cosmologies and creation stories the gods master chaos, YHWH just speaks and peacefully gives creation its being ex nihillo. So the purpose of the text is partially polemical against paganism, etc." Now, by knowing about the ANE background which Genesis is trying to polemically correct, we have in one respect advanced in our exegesis over the Reformers. They knew nothing about said background and therefore they didn't have the insight in this regard which we have on this particular point.
But if we return to dogmatics, has anything changed? No, of course not. The sedes still says the same thing. God made the heavens and the earth. So, the doctrine remains. For this reason, the Ratzi's objection is wrong. First, when better exegesis comes along it does not destroy the article at all- which is what the CA is concerned with. Secondly, because exegesis deals with a different aspect of the text than doctrinal theology, an advance in exegesis does not actually change the article in the least. Furthermore, contrary to the Catholic claim, there is not a bit of ambiguity in the article.
What is most interesting in his treatment in The Principles of Catholic Theology, is that he never argues against the Lutheran exegesis itself, he simply says that lacking a magisterial authority it's necessarily doubtful. Interesting! He also admits the content of the CA is "mostly Catholic." How interesting!