In my opinion, magic defense is needed for all key units: Titan, Rakshasa, and Djinn. I've often found myself choosing a hero with stronger fire magic. I quickly boosted their magic resistance, and then used Fire Wrath, which makes them even more resistant to magic and adds fire damage. The thing is, Armageddon deals minimal damage when created by a hero, around 15-18, which is about -63 percent, plus magic resistance. And if you find Armageddon, you win against your opponent about 90 percent of the time. The only thing is, you need to find Armageddon. This can be used as an alternative strategy. I've tried it three times, and it worked all three times.