The merits of those candidates is debatable, but the prestige of those positions really isn't.
You should also be cognizant of the makeup of the SSG and how it's needing to, unfortunately, evolve. It's far from a homogeneous group. The trading arm has needed to be completely restructured after Volcker came into full effect in July. Trading distressed debt is hard enough when you can take quasi-prop positions, now it's a fundamentally different business and many top traders have fled to the buy-side. I believe the only area that's truly insulated and routinely profitable is MSI, which, yes, I'd be inclined to suggest is a prestigious role. However, that's a small segment of the SSG.
I'd reverse your final sentiment. In my experience, the merits of those in the SSG are usually top notch (just pick the best of the S&T/IB pool), the prestige is debatably if your broaden the discussion. One of the best young members of the SSG just left to go back to school to learn how to code.
Also note that by context for impressiveness in the OP was, for example, to go work at a hedge fund in Mayfair right out of Oxford (perhaps, for example, at Chris Rokos' new fund as he's a maths Oxford alum).
As someone who worked at Goldman and is college-aged, I think this says quite a lot about the piece in general. Working at Goldman is not some kind of prestigious, difficult to obtain position. If you're in investment banking, that's laughable. If you're in the SSG, then that's only more mildly impressive. I did two-weeks in London where a few of the interns were part of the Pitt club at Cambridge (albeit, not quite as storied a group, but Cambridge's version of the Bullingdon Club) and seemed to revel in this prestige despite having decidedly worse placements in every way than myself. Only one of the three members were hired back full-time.
If these kids went to work at interesting hedge funds in Mayfair then I'm inclined to suggest they have some powerful connections. But, by in large, these are 18-21 year olds with all the insecurities and lack of knowledge you'd expect. In the world of finance perhaps this club helps getting you an interview at an investment bank, that's about it. Once you see how these things work you become cognizant of the fact that stories like this are more based in what the members of the clubs want you to believe secretively, or rather a writer would like to suggest is some vast conspiracy to pontificate on his or her moral outrage, then having even the slightest basis in reality.
Now, I would grant that having this kind of network gives opportunities to become more involved in politics (similar to what Cameron himself did) at an early age. That's fair, I suppose, however this notion of these secretive groups, with members who have intellects and connections that the average chap can only dream of ever obtaining is laughable. I'd encourage folks not to be drawn into articles like this, similar to the film The Riot Club, that seek to create heroic tragedies and spark mock outrage. Things are always more dull then they appear and most things aren't intricate conspiracy theories, which unfortunately HN seems to have a predisposition towards chatting about.