Atomic Drop lets him build up Super Armor, which grants him invulnerability to attacks.

Source: https://www.cbr.com/street-fighter-duel-best-character-role-capcom/

Since Saitama’s only skills are his speed, strength, and physical invulnerability, finding a workaround to this can be quite simple.

Source: https://gamerant.com/one-punch-man-saitama-weaknesses/

The most glaring issue with this technique is the element of invulnerability that it brings to the table, coupled with its inconsistent usage.

Source: https://gamerant.com/naruto-why-the-substitution-jutsu-makes-no-sense/