An upright hominid could see better, but could also be seen better. Even now as a species, we are almost preposterously vulnerable in the wild. Nearly every large animal you can care to name is stronger, faster, and toothier than us. Faced with attack, modern humans have only two advantages. We have a good brain, with which we can devise strategies, and we have hands with with we can fling or brandish hurtful objects. We are the only creature that can harm at a distance. We can thus afford to be physically vulnerable.