I can remember, not so very long ago, one UK airline where the pilots took it in turns to do everything backwards and forwards to Aldergrove out of LHR. All PF and PM tasks were undertaken by the handling pilot. This probably doesn't demonstrate the most sensible cockpit management but proves what is possible by one pilot in a multi crew cockpit. Indeed most pilots of a certain generation will have done a pilot incapacitation drill where they were solely responsible for the arrival.
In both cases the PM should have been able to pick up on what was going on and keep himself 'in the loop' by simply monitoring what was happening. If not, it strikes me that they are lacking a certain amount of 'aviation maturity.' I have no doubt that for 99% of pilots, total reliance on automation will ensure a trouble free, if dull, uneventful career. For the 1% who are unlucky enough to have some kind of unannunciated failure that requires some kind of stick and rudder skill, they will be glad that they put their PM under a little pressure once in a while.