Your completely ignoring the point of the article which is about ecology, it has nothing to do with pollution levels. Your points don't disprove what the article is proposing. Hunter gatherer tools are extremely efficient. Spears, bows, fire, fishing nets, and dogs alone put them on a level above anything else on the planet. They did kill off some of the most prominent species on the planet, and there is no evidence to point to that they would stop moving from one to the other without a move towards agrarianism. Their populations did grow. Enough to where they spread across almost the entirety of the planet. One of the points touched on in the article is the rates of infanticide and induced abortion in ancient H-G society to try and slow population growth. Birds can't spread seeds if all the fruit or vegetation has been been picked clean by a group that cares only about feeding itself right now because it has no backup. People purposefully harvesting seeds and planting them in the same area while also raising animals take a lot of strain ecological off the environment.