In all the cases, not a single patient had been given CPR prior to our arrival.
There's your killer factor right there... The article did talk about people receiving CPR right away from a bystander. And that was the case of my colleague's mother too - they were sitting at the dinner table together when his mom's heart went into cardiac arrest, and one of them had been trained to do CPR.
It sounds like CPR is absolutely worthwhile, based on the statistics you quoted - there's a 10x or more improvement in success rate from immediate CPR. However, that CPR needs to be immediate. The obvious conclusion is that more people should be trained in CPR techniques.
In all the cases, not a single patient had been given CPR prior to our arrival. So right there, you can assume at least 5-10 minutes without any circulation. The (very rough) formula they taught us back then: every 1 minute without circulation -> 10% less chance to a successful CPR. When you go into cardiac arrest, you need CPR immediately or that's it.
In Germany the statistics at the time suggested roughly the following success rates:
Now, here's the thing: "Success" in all those cases means nothing more than 'Return Of Spontaneous Circulation' (ROSC). In layman's terms: the heart would start beating. That - of course - tells you next to nothing about brain damage.The elephant in the room is, that when you end up being CPR'd in the street by the EMS after no circulation for 5 - 10 minutes, you better wish that you don't end up with ROSC. Because in all likelyhood you will (if you don't die after a few days in hospital / they kindly pull the plug) end with about as much brain activity as the chair you are sitting on right now.
Again: YMMV and I personally know a guy who was successfully resuscitated and became a paramedic after that. But I try to base life decisions on statistics and not anecdotes, so I personally prefer having a living will set up.