In good bowling conditions it makes no sense to weaken your batting, SA getting what they deserve.
don't believe sense comes into cricket, sides play almost a set line up or 'balance' even though the 'balance' isn't
can be too much 'faith' in capabilities of middle and lower order batting, England at the World Cup might have had a line up if not Ali, Curran, Woakes, Rashid, Topley then similar in terms of all bar Topley can bat but in ODIs I wouldn't be expecting more than maybe 10-15 runs usual and 20-30 cameo sometimes max
Ali and Curran aren't such good, or even for me remotely good enough, bowlers that the 20-30 runs they
might bring balances the bowling which could be 1 or 0 for 50-60 (Ali) or worse, and when batting even if say 240/4 or 5 you want support for any remaining batsman and partnerships which the 10-15 don't really bring, more regular wicket fall
that tail looks painfully long, Maharaj and Rabada can bat but saffers don't seem to have much depth these days, not that the 8-11 should be digging you out of holes when the top order are 34/5, that's a write off, but had it been say 160/5 then that's when a little more depth of batting helps a little - not at the expense of bowling, but how many bowlers are sooooooooooo good you can afford to not take batting into account or stick 3-4 in the side.....?