We've had something of a depth problem for years. It's gotten a lot worse recently. We had Duminy's very capable part-timers and berhardiens very mediocre part-timers to call on. We had Morris who showed a lot more promise as a genuine allrounder when he came in than he has lived up to. And we were playing more bowlers who could bat a little, like Philander. The bowlers we have been blooding recently (with the exception of Andile) have dross with the bat.South Africa has had a depth problem for years. In recent history it's always been a feast or famine top heavy lineup. It's simply been covered by the fact the top 4 were arguably the most destructive top 4 in the game. But with AB slowly losing his skills(and he has been), QDK not being anywhere close to the player he used to be, and the others getting even older, the problem is simply coming to a huge head now. Within 5 years or so, South African cricket as an ODI power is going to be over.
Finished as an ODI power is a big statement. We had the worst series I can remember, but it was only one injury laden series and we had a great run before that (against some admittedly weak opposition). This series notwithstanding, we have a great top 4 who should hang around until the world cup or beyond. Form has been a bit of a concern, but none of the players are old enough to say they are past their best yet (they could be, but it remains to be seen). Miller has got consistently better over his career. And we still have some solid bowlers.
Post 2019 we probably lose about 5 mainstays of the team. We are going to have real issues then, but team strength is always cyclical. 5 years from now, who knows. There will be players we have never heard of. Our domestic structure doesn't exactly inspire confidence, but it only takes a few great players to come through to build a team around.