Only 4 teams have lost by more than 300 runs so far. South Africa, Netherlands, Sri Lanka and USA. Sri Lanka has lost by 200+ runs twice. And both times they lost against India. But yesterday South Africa broke all records. They lost by a huge margin of 342 runs. And I don't think any other team will be able to break this shameful record.
Never expecting to see South Africa at the top of this list. It is a big shame for them. SA could have reduced the losing margin a little if Bavuma was fit to bat. Still, getting all out in less than 100 runs is something unexpected from South Africa while the target is above 400 runs. SA batsmen have failed miserably in the last ODI match. I also think that this shameful record won't be broken by any other team.
We could not have imagined that South Africa would lose the third match by 342 runs, given the way they had performed in the previous two matches and defeated England back to back. However, in the third match, no South African batsman could survive for more than five minutes at the wicket. It is hard to believe that the batting disaster would be so severe without seeing the batting disaster of an attacking team like South Africa. However, I agree with you that if Temba Bavuma had been fit to bat, then perhaps the margin of defeat would not have been reduced and the team would not have been at the top of the list of the biggest defeats in ODIs.