Peuce
You state
... take the safest option (eg Class C)
Class C is only the safest option if it is adequately manned.
The Aussie system of using a Class D Controller who sometimes is very busy to also be responsible for vast amounts of Class C airspace is clearly an accident waiting to happen.
You only have to see what happened at Hamilton Island where a Controller nearly put two RPT jets into each other, and hidden in the safety incident report was the fact that there are other people communicating. I also understand from locals that there were aircraft being held outside the zone.
I believe this is a clear example that if you load a Class D Controller with too much workload, errors can take place which reduce the safety in the D even though you have lulled yourself into a false complacency because we have lots of C above!