I'll try and clarify.
10 years ago, the domestic system produced a lot of right arm fair-to-good medium-fast swing bowlers and because most pitches assisted them, they were incredibly successful taking loads of wickets in the FC domestic tournament. The issue was that most pitches outside of SA are not as green so a lot of them could not step up to next level because their lack of pace. There was also the issue that none added variety so someone like Terbrugge who was similar to Pollock in many ways lost out not only because of injury but because he added nothing new to the attack. I'll go through each bowler you presented.
Terbrugge - as mentioned, right arm medium-fast bowler who could move the ball of the seam but not very quick
Pretorius - one of the promising players whose stock delivery was over 135kph. He had a different problem where he had poor mental toughness
Ngam - Another promising fast bowler similar in action to Donald but of course hampered badly by injury. Ended up bowling of 2 step run up after that.
Ntini - In 2000, he was really quick and one of the few that went on to make a good career because of it.
Willoughby - Medium fast bowler who could swing the ball. Difference was he was left-arm but was not very quick.
Hall - Another right-arm medium-fast bowler. Fantastic bowler in FC cricket where the ball is moving around but failed to make an impression outside of ODI cricket. Also not very quick but able to crank it up to 140 at times.
Bryson - Quick bowler but hampered by age.
Nel - Another right-arm med-fast bowler. Got much quicker around 2003 and then lost it somehow.
Elworthy - Seemed a little quicker than the rest but didn't have much promise for the long term given his age.
Hayward - Probably the quickest out there who was able to hit 150 at times, but had injuries and control issues. Ended up bowling for 3 step run up later on.
Dawson - Another right arm medium-fast/fast-medium bowler.
If you rule out those who were hampered by injury and ages, there weren't a lot going around in terms of good classic SA fast bowling. With Donald losing pace in the naughties, what SA needed was another strike bowler and there was nothing on offer. In the end, Donald lost pace and retired and Ntini had to pick up the brunt of the striking and he wasn't as good and Pollock wasn't a strike bowler. There was definitely something missing in the attack and I think it's the main reason why they were trashed by Australia in 2001. Steyn was also rushed into the international scene because of it.
Now is the same missing from the current bowling stocks? I don't think so. Steyn and Morkel are two great out-and-out strike bowlers with plenty more in the domestic scene. There's also a lot more left-armers and plenty of wrist-spinners. In the past, having someone who was able to hit 145 was a luxury, now I count 4-5 bowlers who can do it consistently (Steyn, Morkel, Alexander, Plaatjies, de Wet). The reason for this IMO, the pitches that are being prepared are flatter hence those who didn't have much pace needed more variety in their bowling or had to gain pace. Someone like Lopsy figured this out where he wanted to gain more pace and succeeded in doing so in Australia hitting over 140. He got injured after that though and now I think he is attempting to be more of a Bracken type bowler who bowls a lot of cutters and mixes his pace.
What is eluding is the 3 seamer option because of the lost form of Ntini, however this is a recent problem and so new options are being tried. Tsotsobe and Parnell have only had a handful of games.