To be honest on the line I see the FO's can handle the A/C in IMC doing approaches. The company does a good job in the Sim getting them ready for that.
Where I see the difficulty is general IFR procedures, radio calls, multi tasking, paperwork, and doing visual approaches. And thinking about the comfort and considerations of the passengers.
The 20 hours of IOE helps...if the IOE Captian cares....and then about 200 hours in the aircraft.
It is like instructing...but it gets difficult if the FO has an attitude!