My cows were never obese nor lazy, they were just well adapted to eat grass and convert it to rich meat and nutritious fat which I eat and nourish myself with. My sheep, well, true, they are vey fat, but still not lazy. Have you ever seen a cow run? They can go faster than us humans and for longer. Ever tried to outrun a sheep? Nope, that is why we use sheepdogs. Being a herbivore does not equate with obesity, laziness or a lack of fitness or speed.
Interstingly, I got obese and lazy when I ate plants. I no longer eat them. I do not do well on plants, of any kind, in any form.
Truth be told we are all different and have our own niche in the world, whether we are great cats or huge herbivores or anywhere in between. Feed a sheep or cow meat and it goes mad. Feed a great cat grass and it starves. Feed humans processed food and we get sick and obese. Each to its own.