The 'TCU only' thing as far as I can tell is/was an anachronism, stemming from the old TAR spinning faster than the old RSR and the old green screen updating faster, 5 seconds verses 12. Oh, and TCU controllers being supermen, in their minds anyway.
True.
The Melbourne Tech's could think of no reason why West Radar could not apply a 3NM separation standard within 100NM. The reference to "TCU only" seemed to be nothing more than ATC politics and a demarcation. Something that we as a profession in Australia have only ourselves to blame.
Some years ago I flew into Marseilles up-the-front (courtesy of BA) and watched on TCAS an opposite-direction aircraft pass 5NM abeam us on descent. The crew told me that the separation standard was 3NM... everywhere.
If Area Controllers in France can apply a 3NM separation standard using similar equipment then why can't Area Controllers in Melbourne?
As for an additional console or two in the Perth TCU... it can be done.
Staffing issues can be solved and it could quite easily become a Feeder Sector for the TCU if not an Approach-Journeyman position. Perth Inners in TAAATS sat alongside Approach/Departures in the TCU during Consolidation. There is no reason why it couldn't happen again.