Sadly "battle field" emergency rostering at GF has nearly always been the way things are done as it is thought to save GF money.
It does however cause a lot of premature mortality amongst crews if done over several years.
I would argue that the relatively high crew turnover rate is the real driving force behind this viscious circle.
For an old airline that has not really experienced any real growth for a long time and an island with a good social life, the last thing one would expect would be crew shortages.