The jet would have been tracking using its FMS, and the PC12 would have TSO'd GPS, so the tracking would have been accurate compared to the NDB/VOR case.
The tolerance of a VOR is 6 degrees, GPS is 7nm (it was 15 until recently) either side of track, regardless of FMS/TSO etc. As I said, these are sep standards, not logic! An aircraft tracking to/from an NDB has tighter nav tolerances than one using GPS. As an aside, that explain the NOTAM about GNSS aircfraft being still required to notify VOR, ADF etc when flightplanning).
ITCZ, yes, if time permits (standard ATC Excuse #1) and there is no other traffic in the way (standard ATC Excuse #2), diverging radials are the solution.
PC12 would have been maintaining F230 wanting descent with at least 60nm to run KU, and the Ejet airborne near KU wanting climb.
In that particular case, on normal climb/descent, would not the PC12 be below F180 prior to the Ejet reaching F180 and needing a clearance? If so, tha passing is in class G and the pilots responsbility. Whether that is a good/safe service, and what it should be is a whole other can of worms!
there might have been a better way to do that.
To be honest, quite often after a busy burst, it's possible to look back and think "I could have done that better", "If I had done this/that so and so could have had a clearance" etc. The busier you get the simpler you keep it, and unfortunately for our customers, the is nothing simpler than NO.
PS
There will always be a navaid at the aerodrome for turbojet departures (CAO 82.5).
Don't tell the guys/girls who fly 146's into Ravensthorpe that!