TCAS only needs a transponder, it does not need ADS-B in the other aircraft, just mode A, C or S. It can't make resolutions on Mode A though as it has no altitude readout to relate to, but it will give a warning of traffic via a TA. The range for TCAS is more than adequate almost always displaying traffic out to 10nm or greater, the display is only for situational awareness, not separation.
With regard to Ballina one point that I've also thought about with the A320 incident described above, is why it's allowed that a pushback can proceed that will block an aircraft vacating the runway. It needs to be written into procedures that pushback can not commence while an arrival may be forced to hold on the runway. This sort of thing can really only be solved by positive ATC control. Or some sort of holding allowance needs to be alerted that aircraft may have to hold for 10/20/30 minutes while RPT in operation to ensure they have adequate fuel. There needs to be coordination if an RPT procedure is going to cause delays due to aircraft size and movement area limitations.
It sounds to me that there is more than just the airborne issues at play here, if CASA is allowing multiple RPT jets into a port that can't handle them to be moving around at the same time without closing the runway strip.