A few years ago, a couple of disgruntled f/a's in domestic challenged seniority in FWA I believe, on grounds of discrimination.
They lost needless to say.
If you are so disgruntled with seniority then lobby the union.
Seniority is in the EBA and approximately 85% of FAAA members voted in favour of seniority when polled recently.
It is not perfect, but an overwhelming majority of crew are happy with it.
Until that changes, get used to it, or transfer to the A380 and see if you get any more weekends off.
I'm sure that you will see work positions by seniority become a thing of the past though once the new EBA is nutted out.