CleanDamageManager.cs

public abstract class Character
{
    public int Armor { get; set; }
    public int Life { get; set; }
    
    public abstract void TakeDamage(int damage);
}

public class Warrior : Character
{
    public override void TakeDamage(int damage)
    {
        Life -= Math.Max(0, damage - Armor);
    }
}
public class Mage : Character
{
    public int MagicProtection { get; set; }
    
    public override void TakeDamage(int damage)
    {
        Life -= Math.Max(0, damage - Armor - MagicProtection);
    }    
}

public class Rogue : Character
{
    public int Furtivity { get; set; }
    
    public override void TakeDamage(int damage)
    {
        Life -= Math.Max(0, damage - Armor - Furtivity);
    }    
}

public class DamageManager
{
    public void CalculateDamage(Character character, int damage)
    {
        character?.TakeDamage(damage);
    }
}