By all the Hells! What were they thinking?
I'm sorry, the Shadow Druid fight was a MASSIVE letdown. It was so easy. It hardly felt like the climax to some sort of side quest story arc. 3 Shadow Druids facing my party of 4 Level 4 characters plus a room full of druids? Really? Even if I hadn't convinced Kagha to side with me, this battle would have been easy. I wasn't even fully rested. My characters were weakened already, and I never took a hit from a single Shadow Druid. Olodan focused on taking out other druids rather than my characters. I walked up to each of the 3 Shadow Druids and beat the tar out of them. The battle was over in 2 rounds.
Here is what they need to do to tweak this battle: More druids siding with the Shadow Druids. Whether Kagha joins you or is against you, the battle should split the NPCs in the room so that it is a 50/50 battle. If I have 4 party members and Rath on my side, and Olodan has 2 Shadow Druids and Kagha, the rest of the druids in the room should be split 50/50; half siding with Kagha and half with Rath and the player's party. If Kagha joins you in the fight, 3 of the other druids should immediately side with Olodan and her Shadow Druids and the rest are then split 50/50 between the two sides so that the sides are kept even. Then the fight would be more challenging and fun and climactic as opposed to just everyone pouncing on 3 Shadow Druids and ending it within 2 rounds. This also makes more sense because as you are wandering the grove you find that some druids side with the Shadow Druids and some don't. So there should be a more even split between the two sides.
Either that, or Olodan needs to cast some sort of Lesser Rite of Thorns to block off all the druids in the room with a circle of thorns so that she and her 2 minions and maybe Kagha can kill you and your party. You, fighting alone, just the 4 PCs battling against Olodan, Kagha and her 2 Shadow Druid minions would be a more rewarding fight. If Kagha sides with you, she gets cut off from you as well by the Lesser Rite of Thorns.
Or, Larian could do both. Have 50/50 split in the druids and have Olodan cast Lesser Rite of Thorns to cut her and her more powerful minions off from the rest of the room. While the druids are killing each other, Olodan and her team battle you and yours. A duel to the death in close quarters combat. Since druids are mostly not ranged, this makes more sense too. They wouldn't WANT your ranged party members climbing up on walls to shoot them from above. They'd want to keep the heroes close so they could turn into bears or wolves or whatever and maul you.