I think viewing "secure attachment" and "positive outcome" as separate effects of the "sensitive caregiver" is misleading. This model suggests does not place enough emphasis on the correlation between the two effects.
First, it suggests that a secure attachment and successful social skills can develop simultaneously, and second, it suggests that "secure attachment" is not necessary to achieve a "positive outcome". While I am unaware of studies conducted on the social skills of individuals who lacked a secure attachment in their childhood, I see these suggestions as inconsistent with the "template" theory. The theory states that the relationship a child builds with his caregiver is used as a template for forming future relationships, suggesting that positive outcomes cannot be achieved without first constructing a positive template and refuting the idea that the two effects can be achieved simultaneously. The theory also suggests that successful social skills are far less likely to develop without a positive template to build off of, making the possibility of a child achieving a "positive outcome" without a "secure attachment" highly unlikely.
While I agree that a sensitive caregiver is essential to the development of a secure attachment, as well as essential to the development of social skills, I suggest the use of a different model: one that presents the three factors in chronological order (sensitive caregiver --> secure attachment --> positive outcome). This model incorporates the two inconsistencies previously mentioned, and represents the relationship between the three factors more accurately.