Sydney, T3, Monday morning about 4 or 5 months ago was TOTAL CHAOS! The lines were out the door. whY (no status) check in was literally a snake winding past the WP check in line, l couldn't see the end of it to be honest. It was total madness.
The QC, SG, WP and 1W dedicated lines were also choc-a-bloc. AND, not all dedicated counters were staffed (which several people had noticed and were making a point about). A point which the OP is making here, l think.
Could happen anywhere; but on a Monday morning, (peak hour in my books), QF should know in advance about loads on flights and make adjustments accordingly with staff.
Since I've only taken that flight to PER on a Monday once, l can't really say if it happens every Monday and l try to fly in the afternoons.