These 'staff shortages' have been going on for years - it must be 7 years at least.
If controllers are doing enough overtime to keep things ticking over for the past 7 years (with the odd TIBA) it would seem that maybe there are only staff shortages in some peoples eyes.
Maybe the system is working just how management want it to. If people are willing to waste their lives doing overtime - who cares let them do it. That is the system and many Aussie ATC's think the overtime is just fine.