The lesson Evangelicals should learn from this new dust-up over evangelical theology and modernity is that sola scriptura is necessary but not sufficient for maintaining theological orthodoxy. Only a “single-source” view of scripture and tradition in which hermeneutical authority is given to the mutual interplay of Scripture and orthodox community—the method that the church practiced for most of Christian history—can protect evangelical theology from going the way of all flesh, to liberal Protestantism.
Post-conservatives claim conservative Evangelicals elevate tradition—both evangelical tradition and early church tradition—above Scripture. But Great Tradition Evangelicals say they want to submit their individual interpretations of Scripture to those of the wider and longer orthodox church, and interpret Scripture by thinking with the Great Tradition.
You can read the whole thing here. One could add to Professor McDermott's conclusion--and he may very well be implying this--that Scripture itself arises out of the Church and its practices, and thus it is itself, not so much a product of tradition, but authoritative writings that were recognized as such in an organic relationship with the Great Tradition.