It wasn’t gratuitous in the context of the show. They were attacked by said troll. The troll attack advanced the plot by serving as a catalyst for Galadriel’s

It wasn’t gratuitous in the context of the show. They were attacked by said troll. The troll attack advanced the plot by serving as a catalyst for Galadriel’s troops deserting. Unless you’re saying that just having a fight scene with a troll was gratuitous? But the books have plenty of battle scenes with trolls as well.