If a child builds a strong bond with a "sensitive and supportive" caregiver, that child will benefit, being more attached in her childhood and more socially successful and attractive as an adult.
I wonder how causality may be linked to her relationship to that caregiver as an adult. The relationship will likely develop into more of a peer-peer relationship, but the root of that relationship gives her support and comfort, even as an adult. Perhaps the longstanding evolution of this positive relationship is a cause of the adult's continued success.
I agree with what you said about attachment, but I don't fully agree with your statement that a relationship with a caregiver would turn into a peer-peer relationship. I thought if the caregiver were to spend that much time with a child that a secure attachment is developed then it would be more along the lines of parent-child.