Why do all of the BASSA hardcore believe this rubbish?
Because they have to believe
something so that they can convince themselves they've won the dispute. You'll notice how the reason for the dispute was originally 'imposition'. Now that it's clear the imposition will stand the reason has been massaged into 'union busting' so that BASSA can claim that they are still in existence and have beaten BA. Never mind that they are still working one down and Mixed Fleet are growing every month, as long as BASSA are in existence (and largely ignored by BA) they'll paint it as a victory. It was never about union busting, it was about getting the required savings and BA have achieved that in spades.
PS. The strike was quickly beaten: twice in court and then over the 22 days of actual industrial action. Flogging the same dead horse repeatedly doesn't make it a victory for BASSA. BA have already got all they wanted.