So is there any real justification for the fare increases or are they just being
mean?
It's more to do with how effectively we have a duopoly. Both have decided it's best to (depending on the route) reduce capacity (two examples would be MEL and SYD across to PER), increase capacity but at less than the market is growing, soaking up some empty seats (a strategy they'd probably both like on lucrative golden triangle routes like MEL - SYD) or keep the number of seats stagnant. This in theory allows both to raise fares (although as JohnK is correctly implying, above a certain price that could mean some discretionary passengers simply don't travel and the number of empty seats trends upwards.)
At times, the duopoly manages to increase the number of seats perhaps a little unexpectedly (for instance if I'm not mistaken TT recently commenced MEL - CBR - MEL) but generally capacity seems to be fairly tightly controlled.
harvyk would not be the only individual doing what he outlines as a possible response.
Slowly the number of tourists from mainland China seems to be coming back (in other words, previous increases each month have become lower) so whether that continues is a $64 million question. If that source starts to decline, it will have quite some adverse effect on both airline groups as one sees these tourist groups on offpeak flights in the golden triangle, and presumably any flight on other routes such as CNS - AYQ and BNE - CNS to name two.
It's hard to see Australia ever having three major airline groups competing again as every time this has occurred in the last 30 years, the result if I'm not mistaken has been amalgamation or one of the three folding. Compass Mk I, Mk II, Impulse Airlines, EastWest, Ansett Australia, Air Australia (Strategic Airlines)...