Both Gay and Bertans can stretch the flaw. Gay however can post up his man.
I see the two interchangeable pieces in the lineup is at SF and at C. SF - Gay or Bertans, C - Poetl or Gasol.
A 2nd lineup with White, Mills, Belinelli, Bertans, Poetl or White, Mills, Bertans, Cunningham, Poetl has no player that can post up or no player that can individually create their own offense (verdict still out on White if he can do this).
Walker may be a player that create his own offense. We won't know that until he learns the Spurs system first!