Framer this sector had been operated many times by pilots who would have experienced similar disrupted sleep patterns yet managed to get to and from Singapore. This was not an emergency situation but a routine operation which became a problem when the PIC did not do his job or accept his responsibility. There is no mention of the PIC being fatigued. In fact if he was doing his job properly he would have been monitoring the F/Os performance throughout the flight. It was not suggested in the report that the F/O felt pressured to fly home but that he took two controlled rest breaks.
As to my statement regarding "what they inherited" you answered your own question earlier in the thread.