I tend to think of these kind of teams less like squads with positions, but in terms of roles. In a back six IMO you need a lockdown KPD, a lock down small defender, a third-man up type interceptor, a mid-sized hybrid defender, a rebounding defender, and a CHB type with a bigger tank than the lockdown KPD. Seventh defender on the bench is just the next best defender.
(BTW IMO that is Scarlett, N Smith, Stewart, Enright, Hodge and Rance. Seventh no idea)
I think ideally the best teams have two rebounding defenders. I remember Kennelly/Malceski together were such a weapon for the Swans, and later Shaw/Mattner too. Not saying any of them are in contention for this team, but the two rebounding defenders worked well for us and I think work well for any team that has them too (if they are good quality).