LordViRuS, an Orc might be able to defeat the entire Necromancer's army before the Necromancer hero even gets a turn. What mines are you talking about? How many can you set up, and what impact will they have? Berserkers on centaurs or controlling Cyclops – sometimes that's the only thing that can help. That's the way it is.
Besides dark magic and a sharp mind (logistics + education), a Necromancer can, of course, take attack skills for tactical purposes, to reduce the number of troops that reach the rear, or defense to hold out longer until Battle Potion is available.
LordViRuS, watch the replay and tell me if mines would have helped the Necromancer in this situation...
But a sharp mind combined with control would have helped... Of course, the armies aren't equal, but the principle is important... Orcs are capable of defeating even larger stacks...