The main purpose of both of these builds is to cause burning or poison damage, which is not influenced by any defensive metric or skill. It is raw, pure damage to your opponent, there's only one skill that can actually lower the damage from Black Arts and that is common knowledge.
Black Arts is a Unique Skill, meaning it can only be utilized by two rare heroes, Sima Yi and Zuo Ci. This skill is awesome because it not only causes poison damage, but it also strikes up to five units in one hit. The range of effect it uses is in the shape of a cross or a +. For this skill you can find not only gears that increase it's launch rate and effect but you can also find what are called "Specialty and Proficiency" scrolls to teach heroes skills that further increase it's effect and launch rates. Not only that but you can also commonly find Black Arts scrolls in the stand, especially when you use the 10g option. It's not uncommon to see heroes with this skill level 4+. To increase the effect of that poison, which is primarily what we're going to use this skill for, we need to have high intellect on our hero, higher intellect than that of our targets preferrably. Especialy if yo're planning to use either of these two heroes as the Chief Strategist, then focus all your efforts into Intellect. Also, increase that skill level as high as possible, and look for gears, and scrolls that further increase the launch and effect. Enchance your hero looking only for the highest intellect stat.
This skill, learnable by all heroes, found in the Last Man Standing Arenas, can easily tilt the odds in your favor, especially considering the tanky heroes we're seeing nowadays. That burning, consuming flame is armor negating, meaning the only thing that this goes against is HP. Pure raw damage, but only when the enemy moves next, so it is important that you can make sure to hit with this skill at least once a round. In order to do that you'll need to keep an eye out for gears that help increase it's launch rate. When you do hit, you'll want it to do maximum damage. To acheive that result you'll need super high leadership stats, and you'll also want effect boosting gears. So keep an eye out for those as well.