Something to consider for your argument.
To analyse a safety system, you cannot prove it to be unsafe by demonstrating that another system is safer.
The accident at Benalla shouldn't have happened within the airspace system as it was at the time of the accident. The solution is not to implement a new system. The solution is to analyse the existing system to determine why (all things operating as intended) the accident happened in the first place.
If you don't determine the reasons, there is a chance that the latent error in the old system transfers to the new system. This is exactly what is occurring at Ballina right now.
Have you considered that mid air / CFIT accidents happen in the NAS system as well? What will be your argument when after introducing NAS you get the same type of accidents (and you will).