SA could easily have won each of the WCs of the 1990s, and obviously the 2002/03 one was at home so with a better reading of a D\L sheet they could've won that too. I don't think there's any less-than-sum-of-parts-ism about the team, it's just often one tiny mistake has cost everything at the crucial moment.
And in Tests, they have - 1993/94 aside - been been second-best to Australia. Almost all the rest of the time, they've been better than everyone else. The only loss at home to someone other than Australia was England in 2004/05 which could easily have gone the other way, and almost all the losses away not in Australia have come in India and Sri Lanka, where almost everyone struggles. They've played 12 away series in places other than Australia, India and Sri Lanka since readmission and won 7 (drew 3, lost 2 - the losses being England 1998 and Pakistan 2003/04, and the latter too should've been a draw). That's more than acceptable.
Also, they've won in India (1999/2000) and drawn in Sri Lanka (2000) once each - no mean feat. Precious few other sides have managed that.
It's quite natural and to-be-expected that someone who supports them will have the natural anxiety about how they're going to perform. Not at all surprising.