Routes which can be operated non stop from JNB to premium destinations and have only the other country’s airline as direct competition should be profitable, with Ethiopian Airlines lower cost base. Many pax would prefer a direct flight over a connecting one and without competition, fares will inevitably increase. Imagine what BA would charge if they had the only non stop to London.
SAA have the same problem as Qantas, located at the end of the line with no connecting market to serve. Ethiopian are much better situated to provide transit options between different countries. Post COVID-19, they might benefit from the reduction of Emirates size and schedules, EK need enough pax to fill a B777 where as ET only need enough to fill B737s or B787s.