"Weak demons"??

There’s no need to enable quick combat. You need to control it yourself. It is certain that ranged units, in this case, Adepts, will target ranged units (Demons have a Succubus and Succubus upgrades). If there are no ranged units, they will target Imps and their upgrades. Therefore, before the battle, if you are not sure that everything will go without losses, remove the Imps from the battlefield. You don’t need to remove the Succubi; they are already strong, and they also retaliate.