In 18 years and several airlines, only my current one seems to give any thought to preparing FO's for the left seat and that is done by making the operating sector the responsibility of the operating pilot subject to veto from the skipper if you do anything daft.
Sure the skipper will veto when anything daft happens...
But is rejecting a visual approach on a cavok day and instead asking for a 25nm final daft? Extending flaps at 30nm out? Pulling speedbrake when already below profile?
None of these things endanger the aircraft or its occupants.
The problem with the really inexperienced guys is that they often leave a very big margin for error which makes the operation inefficient. Which leads to problems when they do end up hot amd high. This goes pretty much unchallenged and the next thing around the corner is command.
Leaving the entire operation to the other guy is not the same as mentoring... but how far should a normal line captain push?