The security system of the Sang Kendrica city was not bad and as soon as the beasts appeared around it, the higher ups of the city were notified of the danger. Immediately both soldiers and heroes were dispatched on the front lines to fight against them. Soldiers of the city were not going to fight the beasts head on and instead they were going to assist the heroes from the walls with the help of modern weapons.
Beasts were obviously more physically fit than the humans and it was almost impossible for a human to reach the same level as a beast in this aspect. The population of beasts were also significantly higher than the humans. So, even without the heroes, the normal beasts themselves were very much capable of destroying the whole humanity if they attacked together.