First of all, SA has put 10 teams in the second round on the last 10 years, not 7. But let's suppose 16-7 was correct.
Europe 16 - South America 7 is pretty bad for Europe considering UEFA puts three times as many teams as any other continent. The best way to analyze the thing is to get the % of teams that make it to the second round considering the % of teams they get in the compe ion. On that basis CONMEBOL is head and shoulders above any other confederation.
Either way, none of this (what I'm saying, nor what you said in the post above) has anything to do with the fact that, right now, SA has 8 of 10 NT that could pretty well make it to the second round of a WC (this doesn't mean they would make it, just that they are compe ive enough to have a chance).
How do I know this you ask? 'cause in the last two WCs (meaning, more or less the same generation of players as nowadays) SA got 10 of 11 teams in the second round, and the only one that didn't make it, almost made it.
Those teams that made it (Argentina, Brazil, Chile, Uruguay, Paraguay, Colombia) still mantain that second round level. The one that almost made it, and that made it in 2006, (Ecuador) is significantly better than 4 years ago. And Perú, even though hasn't even made it to the WC in the last editions, and won't make it to Russia either because of the insane compe ion, is on the level of any of the teams I mentioned. So, there you have it: 8 of 10 NTs that are second round level. Not that hard to understand, unless you want to downplay CONMEBOL for some reason.