How do we find out if someone has no idea until it hits the fan?
The Check & Training system is supposed to be the filter to weed these problems out. They should never get cleared to line at that level of competence. If they manage to slip through that filter, the on going recurrent training should have exposed the problem. Then it should be either adequate re-training or, if they are unable to reach a satisfactory standard after a suitable period of re-training, the unfortunate situation of letting them go.
Unfortunately the check & training departments of many airlines have been watered down so much that this is what we can now expect into the future. The 'PC' brigade, the 'unfair dismissal' brigade & the 'near enough is good enough' brigade all have to share some of the responsibility. Airline flying is a serious business with serious consequences if you get it wrong, which is true to some extent of all forms of aviation. However, some seem to feel that this is not the case & we can all be a little casual in our approach to it. The old term 'Aero Club with jets' springs to mind.