The real point of CPR is to bridge their life while you rush to get them an AED. Without the AED the chance of their heart restarting permanently is vanishingly low ... Last few times I had first responder training it was said to be less than 15% chance of survival for a patient given CPR, and you'll only hear about this if you ask.
The last time I had first responder training the guy sitting next to me was drowned by a surfing accident but it was his great fortune that on shore there was a national expert giving rapid water rescue training and they had this guy out of the water and his heart restarted in 5 minutes. So that is why he was taking first responder training himself!