The whole idea of regulatory oversight, CRM, SOPs, multi-crew etc. is that no one person can make an error of judgement and cause a serious accident.
But the problem is they had minimal or no training in these fields, they were constantly mixing duties (changing roles from PIC to F/O between flights, or from nav on T154 to F/O on YK40), and their experience (flying time) was very low - it's all in the report. You're right about the idea of CRm etc., and that's exactly the point - they failed in that area.