Why heroes are physically stronger than average humans
In a lot of anime, humans just have more durability than real-life humans. Not sure how I'm supposed to provide sources for this, but in, for example, One Punch Man, Saitama was repeatedly beaten down by Crablante before gaining any powers and survived. In JoJo Battle Tendency, Mark gets half of his head sheared off and is still able to talk for a while after. It's just a common thing in many anime that humans have higher-tier durability than their real life counterparts. I wouldn't pay much attention to this.