With the release of version 3.1, the summon spell for the Warlock became even more relevant than Chaos. The fact is that now, neutral creatures don't wait for the hunters to appear; instead, they run forward to find them. There isn't enough time to kill them with Chaos (or Lethos's Plague). If you have the summon spell, they will rush towards the mines and attack the elementals (you need to upgrade the Fire Warriors), instead of searching for the hunters. You can also use the mines to summon a Utopian.