As strobes_on points out the complaint is very political. Both DJ and QF are desperate for SAC to lease each of them half of the AN terminal. At that point they would effectively control the slots even though it is unlikely DJ are anywhere near needing 8 gates at SYD presently.
The threat of a new Star competitor means the situation is more desperate and SAC's arm is strengthened in any negotiations.
As has been said many times, a new competitor is financially a worry to QF but is financial poison to DJ's shareholders who would see their potential windfall in any DJ float massively shrunk should a third compeitor get up.