This passage assumes that all types of personalities are in need of transformation. It's not just the lazy or the arrogant who need wise leadership and careful correction, it's also the compliant and the quiet. But the very presence of all such persons in the vowed community shows us that transformation is available to everyone who places herself on the path.
In order for the superior to effectively, as Sr. Joan's translation puts it, "vary with circumstances" the means of spiritual formation, there needs to be a clear vision of that into which we are being formed. Our Father Benedict lays out in the Prologue his vision of spiritual formation as a process by which the soul is made fit to dwell with God where God is at home. This is what St. Paul speaks of as "be[ing] conformed to the image of [Christ]" (Romans 8:29), who is fully at home in God's tent (Psalm 15). Like Jesus, we are welcomed into the household of God as beloved children and commissioned to realize our soul's divine calling, our true vocation. Our vocations are manifestations of the likeness of Christ filtered through the particularities of our being. Our unique vocations flow out of and participate in our ongoing process of transformation.
It is this process in the lives of the sisters and brothers for which St. Benedict lays responsibility on the shoulders of the superior.