I think that the main advantage of lower flap setting for approach in gusty/ crosswind is slower reaction aircraft on changing in sideslip.
In gusty wind sideslip is continuously fluctuating and aircraft is continuously banking from side to side due to static lateral stability.
(see
http://aviacom.ucoz.ru/Book_13_Principles_of_Flight.pdf, Chapter10, page 302)
All contemporary aircrafts have swept wing and this lead to excessive static lateral stability (see pages 306, 307 and figure 10.62).
The more Cl (coefficient of lift) we have - the more "dihedral effect" we have, and we have to counter the more sharp lateral aircraft movements.