Wizofoz
We (CX) operate the ER,s to JNB in the winter with similar flight times of 13 hours return. We do it nonstop but I will concede that the payload is very limited. It isn’t the ideal aircraft for the sector. By far the best aircraft we operated there was the A340-600 but they are now history.
Just for interest we operate the ER’s nonstop to JFK from HKG with a similar sector length to you DXB to SFO. These flights too are limited to a ZFW of about 220T because they are at MTOW. That unfortunately is the nature of ULH ops though.
So do I think Vaus can operate the -300ER’s nonstop to and from JNB from MEL? Yes. Are they making money? Questionable, especially with the sector time to JNB.