You can view previews of Heroes in each Summon Gate. To view these, tap the question mark (?) that is in the blue box.

These previews show each Hero at its maximum in Level, Ascension and Special Skill.

Your Hero will only have the same Damage Level as the preview once you have fully Levelled up (including the Special Skill to 8/8) and Ascended the Hero.

This only applies to Heroes who deal damage with their Special Skill.