As long as the membership are willing to settle for whatever BALPA serves up, they deserve what they get.
If the membership is not happy with the representation, then change it. Surely the mechanism to do this exists.
BALPA is there to serve pilots, not vv.
As the textbooks will tell you, union success is not based on logical reasonable arguments, it is based on power, and more importantly, the perception of power.
Logical arguments are merely the justification (or pretext) for using, or threatening to use, the power.
Employers react to power plays, not clever arguments. Sad but true.