If they've completed line training and successfully checked to line, isn't that saying they've reached the required standard to competently operate as a first-officer?
On the day they demonstrated they could fly within the required tolerances. That may be a series of sectors in CAVOK from ILS to ILS, or it may have been something more challenging.
However does that mean they can adequately support a Captain going in to a non-towered aerodrome at night for a non-precision approach with traffic and weather on the minima the next week?
You are correct, everyone does need to start somewhere, but does it really have to be in the RHS of a high capacity RPT aircraft? I suspect that accountants simply point to Europe and the apparent success of cadetships direct to RHS HC-RPT. There is a huge difference - a low vis departure to a CAT III autoland is a procedural flight from the FO as support pilots point of view. It is a series of yes/no decisions and calls that can be learned by rote. It is an entirely different proposition to the complex scenario above. That requires active management of the external world beyond the aircraft by the support pilot & requires judgment & experience in order to provide adequate support for the Captain. Not only is the FO there to provide support - he is also the vital cross check on the Captain. Captains make mistakes too.
Operators that have direct entry cadets that have SO's/ Cruise FO's provide a much better environment. They get to see how to operate multi-crew, the normal flow of the flight and simulator time to practice and make mistakes - mistakes are an integral part of the learning process. At least in this country we have a diverse range of operations to provide an excellent learning environment before stepping up to HC-RPT.
So yes, they may have passed their check ride to the minimum required standard - but is this the way we really want to operate? How are Jetstar going with their cadet program? Are the cadets flying with training Captains for a considerable period of time beyond what could reasonably be expected to make the line standard? If so, there is a reason for that, we have a different operating environment to Europe.