In One Punch Man, the true strength of Saitama has yet to be accurately recognized. Naturally, his achievements are still on the rise. Evidence shows that he has the potential to advance from Class C to Class B. In the webcomic version, he even aspired to become a Class A hero.
Why do people still undervalue Saitama’s strength?
1. Saitama does not boast about his achievements

In One-Punch Man Season 2, Episode 2, it is explained why Saitama is not recognized as a Class S hero. Saitama is always ready to face any monster he encounters on the road; however, he never reports his victories to the Hero Association. This clearly indicates that Saitama’s rank has been rising slowly.
2. Saitama makes monsters feel “not strong enough”
Genos specifically points out that despite Saitama not reporting his actions to the Hero Association, he still ranked up to Class B, placing 17th at the start of Season 2.
This means there is someone representing the association who is actively observing Saitama’s actions. But why doesn’t the observer grant Saitama a higher rank?
The answer is quite simple: Saitama’s overwhelming strength makes the monsters he faces feel “weak.” In reality, very few people know about Saitama’s true power. Therefore, in the eyes of the observer, if Saitama – a Class C hero (and later Class B) – can easily deal with monsters, those monsters must be weak. Even though those monsters could be at the Quirky level or even Rank R.
3. Many of Saitama’s achievements are mistaken as King’s achievements
This is the most straightforward reason why Saitama is not recognized as a Class S hero. Saitama’s achievements, particularly those he attained before becoming a member of the Hero Association, are often attributed to King.
King himself may not be powerful and doesn’t do much at all, but he never denies the achievements that surround him.
4. Saitama’s appearance is too ordinary
With a face that doesn’t stand out and a costume design as simple as a tracksuit, Saitama’s appearance is quite ordinary compared to most other heroes. This is also a factor that makes it hard for Saitama to “break through” the perception of others. As a result, King being recognized for Saitama’s achievements is more understandable.
When observing the failures of the difficult-to-handle monsters, the members of the Hero Association can easily think that King (the one who appears to be tough while facing the beast) has “taken care” of them, but not Saitama who looks too ordinary.