I think what this thread shows is that most don't understand that once an EBA is above Award everything is just an "agreement". The Union or Employer puts together what they think the pilots want, put it to vote, and you either agree or disagree, you duke it out over the finer points and shake hands, at pilot level of pay there is very little right or wrong, it's just what you agree to. Anything that is in continual disagreement will have to be reconciled to allow agreement, the last resort being PIA or just leaving for greener pastures, even then there is no law saying that with every negotiation the EBA must improve, or has to meet CPI (unless you are going to be below relative Award for the industry). The extra 2 weeks leave was added to many EBA as part o the compensation for shift work/working public holidays, that was when agreements were moving out of the dark ages. You do not always have to trade something, that is productivity or such for increased income, you can just claim it as necessary to maintain or even improve workforce desired lifestyle. That does not mean that an extra 2 weeks leave is still worth what it was worth back then, however that is probably how your employer will look at that clause.
The only time you have to justify the increases is if it went to arbitration after an impasse and each side has to justify it's position. Trying to justify claims to the boss is a waste of time, they will always look for the minimum they can get away with, mostly they only ask for the claims justified as stalling tactics to draw out negotiations. Presently the main concern for the workers side is that you are not made worse off by the new EBA and things to be considered will be offsets for days off/public holidays, work specific complications and dangers etc etc... Now worse off compared to what is where the outcome could be good or bad, as that becomes what is the industrial flavor of the day and what the judge/panel orientation is. So just pushing PIA until it gets to the point of government intervention will probably not end well.
None of that stops the employer from outright rejecting an EBA and offering anything it wants and dealing with the pathetic comebacks the workers have, like non disruptive PIA. AJ proved what an employer can do if they really want to, that was against some very mild PIA, and the QF pilot body showed it didn't have much to kick back with.
The best recourse to deal with miserly employers is to just pack up and leave... nothing can stop you from doing that, and if the company can not replace you then they can't blame anyone but themselves. Remember anything you do to 'cost' a company more than doing your normal job would be considered unprotected industrial action, and the company could seek to reclaim lost income from individuals, so be very careful about being too militant without union support.