I don't think the ER4T diet states that if if you follow the diet you will "be a hunter-gatherer" - you may have misunderstood something there. And your not understanding something does not necessarily make it "hogwash".

What the theory in fact argues is that Blood Type O evolved at a time when our human ancestors lived a hunter-gatherer lifestyle and therefore our bodies adapted to digesting that kind of diet (lots of meat). Blood Type A on the other hand evolved when human started living in settled communities when farming was invented, and are hence better adapted to a diet high in vegetables and grains but low in meat.