Worshipper – “Conquest” [Campaign 2, Mission 3]

I understand that we are talking about the source of druidic magic (or whatever it was called), and its destruction is one of the tasks of the mission. It needs to be destroyed at the beginning, so that the elves will not have such a huge army.

This is a secondary task - it can be skipped. I won't argue, because I didn't complete it. Perhaps you are right that if you complete it, the elves will have a weak army. I probably wouldn't be able to defeat the main enemy with just one Agrael. I played through it twice - both times, a hero - a druid hired in the tavern - weakened him significantly. In the second playthrough, he managed to level up on neutral creatures to almost level