While I completely agree with the quoted passage from the WCF, I would add that Creeds perform the necessary function of refuting errors. As the Formula of Concord states,

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FOC, Epitome, Rule and Norm

] 1. We believe, teach, and confess that the sole rule and standard according to which all dogmas together with [all] teachers should be estimated and judged are the prophetic and apostolic Scriptures of the Old and of the New Testament alone, as it is written Ps. 119, 105: Thy Word is a lamp unto my feet and a light unto my path. And St. Paul: Though an angel from heaven preach any other gospel unto you, let him be accursed, Gal. 1, 8.

2] Other writings, however, of ancient or modern teachers, whatever name they bear, must not be regarded as equal to the Holy Scriptures, but all of them together be subjected to them, and should not be received otherwise or further than as witnesses, [which are to show] in what manner after the time of the apostles, and at what places, this [pure] doctrine of the prophets and apostles was preserved.

3] 2. And because directly after the times of the apostles, and even while they were still living, false teachers and heretics arose, and symbols, i. e., brief, succinct [categorical] confessions, were composed against them in the early Church, which were regarded as the unanimous, universal Christian faith and confession of the orthodox and true Church, namely, the Apostles' Creed, the Nicene Creed, and the Athanasian Creed, we pledge ourselves to them, and hereby reject all heresies and dogmas which, contrary to them, have been introduced into the Church of God.

Now, when Calvin and other Reformers proposed a new interpretation of the Creed that retained the form of the Creed but denied its substance (that Christ actually did descend into hell), the Concordists could have papered over the difference (as Calvin did) in order to maintain a false sense of unity. Instead the Concordists publicly refuted this misinterpretation of 1 Peter 3:19 in a binding confession.

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FOC, SD, Christ's Descent into Hell

And since even in the ancient Christian teachers of the Church, as well as in some among our teachers, dissimilar explanations of the article concerning the descent of Christ to hell are found, we abide in like manner by the simplicity of our Christian faith [comprised in the Creed], to which Dr. Luther in his sermon, which was delivered in the castle at Torgau in the year 1533, concerning the descent of Christ to hell, has pointed us, where we confess: I believe in the Lord Christ, God's Son, our Lord, dead, buried, and descended into hell. For in this [Confession] the burial and descent of Christ to hell are distinguished as different articles; 2] and we simply believe that the entire person, God and man, after the burial descended into hell, conquered the devil, destroyed the power of hell, and took from the devil all his might. 3] We should not, however, trouble ourselves with high and acute thoughts as to how this occurred; for with our reason and our five senses this article can be comprehended as little as the preceding one, how Christ is placed at the right hand of the almighty power and majesty of God; but we are simply to believe it and adhere to the Word [in such mysteries of faith]. Thus we retain the substance [sound doctrine] and [true] consolation that neither hell nor the devil can take captive or injure us and all who believe in Christ.