Would there be any loss to balance or gameplay if animals did not have to be killed by villagers to be harvested?

It seems so lamey that if, say, a scout kills an opponents sheep it rots instantly. And it just seems dumb that if villagers inside a TC kill a boar the boar is magically impossible to harvest, it's not even a different unit.

Anyway, is there any real reason why this system exists? The Dark Age would run way smoother otherwise, would there be any significant drawback to changing it?