Vilas,
I disagree.
The OP asked a question of the FCOM. I explained my reasoning using an official source. I didn't use hear say from an instructor, I didn't use the FCOM to explain the FCOM (narrow body Airbus pilots already have an FCOM and can read it) I didn't even denigrate the FCOM "it even goes to the rediculous extent of selecting Config3 when flaps are jammed where you only move the Flap lever to three when nothing else moves."
I cited an official source which explained lateral gain control in Conf3 and Conf full.
Cite an official source backing whatever claim you are making, then I will listen. Until then, landing Conf3 is because of lateral stability - no other reason.
Regards,
Mongo