This information is usually received whilst taxiing out and then the take-off data is calculated and setup.
Incorrect. The takeoff performance is calculated before pushback using the provisional data. 9 times out of 10 it covers the eventual actual TOW and no reprogramming is needed. The ACARS final figures will come through as 'CHANGES' or 'NO CHANGES'.
The general principles work well and save the time getting a final loadsheet to the aircraft.
The issue at FAJS and FACT is to do with the time in getting the numbers back to the aircraft. This may well be a dispatcher issue at these stations as generally it works quite well at most places nowadays. There are comms issues with the handling agent at JNB and at CPT there are issues with the generally short taxi out time and no holding area which can be embarassing. For that reason, some of us won't push straight away but give it a few minutes at CPT.