Don't be thick. Life was much more iffy 300,000 years ago. Human beings, regardless of their beliefs, are not the top of the food chain. In addition to predators, disease, malnutrition, whatnot, took their toll. If we were to extrapolate your calculations to other species on this planet, we should be up to our eyeballs in flies, rodents, and guppies.
Except that they all have predators. They have limited breeding grounds, they are killed by changes in weather, etc. Man with tools is the top of the food chain except for disease and parasites.
Sure without agriculture man would be limited by the food supply and periodic famine. But the earth is still capable of supporting a lot of men without agriculture, and we just don't see the record of lot of men having been around for 300,000 years.
Hell life was iffy just 150 years ago. It was nothing to lose a family to cholera or smallpox or bubonic not to mention stillborn or short lived infants. Then there was war, starvation, and outright genocide on top of that.