Low Defense is Zero Defense
A Low Defense is Useless
Armor has a zero effect when less than the enemy armor penetration
Magic Defense has a zero effect when less than the enemy magic penetration
Beyond that point:
** 0% less damage when less than enemy penetration
** 25% less damage when 1000 above enemy penetration
** 50% less damage when 3000 above enemy penetration
** 75% less damage when 9000 above enemy penetration
Do Not Build Useless Stats
Most heroes have either a max armor or max magic defense so low that they will always be way below the penetration of most of their opponents. There is often no benefit in increasing them
Physical characters typically have an insufficient magic defense, while magic ones have an insufficient armor. Tanks are the exception
Some powerful heroes have low penetration, so you may want to go the extra-mile against them: Helios, Yasmine, Lara, or to a lesser extent Dante
Augustus is quite peculiar because he focuses the hero with the lowest magic defense
How to Check?
Go to a hero page such as Dante and click on his armor score, you will see a calculator like this:
