I could have sworn that Summon Darkling had a cooldown before. I started a new game. The closest enemy pack was 3 Darkling Shamans (2 ATK, 14HP, 0 DEF). My sov, spearmen and militia. 

Each turn each shaman can summon 1 Darkling Warrior (2 ATK, 0 DEF, 7 HP). The new stamina mechanic means I need to build stamina to use the Impale ability which in most cases the only way I can kill all three summoned warriors in a round. Meaning I am not doing any damage to the Darkling Shamans creating them. Killing a shaman doesn't eliminates it's minions. 

Basically my rounds looked something like this:

Started fight with 3 shamans

Unable to attack either shaman. 3 warriors summoned. 3 shamans and 3 warriors on the field

Unable to attack any of the shamans, killed 1 warrior. 5 warriors, 3 shamans on the field.

Killed 1 shaman. 2 warriors summoned. 2 shamans, 7 warriors summoned.

... this is an overrun. 

Although, this is an encounter that I now know to avoid until I have better armies I'm going to assume that this will spawn "raiders" of a similiar difficulty and that might be too rough for low some players. 

I would recommend  pushing the minimum distance for this encounter to the midrange.