Natural grazing is not about single animals, it’s about all. Both in numbers and in species.
Our landscapes used to be rich in wild herbivores. Many species coevolved, all claiming their own niche. In spring and summer all animals have one big feast. Plants grow rapidly leaving a food supply for many. Some animals might even facilitate others. Autumn and winter are times of scarcity. Animals are competing of the same food resources. Some migrate to other areas, others search for different niches. Leaving out one species is having one niche unfilled.
Natural grazing is also about natural numbers. Human hunting severely lowered grazer densities. Having to few animals leaves many niches open. Open meadows full of flowers, insects and birds, turn into forest rapidly if without large herbivores. Uneaten plants dry out in periods of draught or winter, rapidly building a huge stack of biomass ready for a big forest fires.
Finally natural grazing is also about predation. Predators selecting weaker animals, strengthening the overall condition of the herds. As a rule large predators are seldom able to control prey numbers directly. For predators to survive there must always be a surplus of prey animals, because there are always individuals to fit and to strong to take down. But predators do have an effect on the behaviour of prey animals. Areas with high risks are avoided, having different vegetational growth compared to areas with less risk. Predation also promotes the occurrence of mass birth, as this lowers the risks for individual calves and foals.