And there is no gratuitous killing of trolls in the source material either.
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.
They are not elite fighters in the sense of, say, just being a Navy SEAL.
If you're looking at Rings of Power and expecting a being such as Galadriel to break a sweat fighting something like a troll, you have a strange set of expectations.
Which is why it's s suprising that a frost troll took out 3 of them in one lumpy throw of some packed ice
I don't think that's consistent with the fights in the books.
I mean Fingolfin physically fought a 40+ foot tall Morgoth in the Silmarillion. He was jumping around between huge pits that Morgoth's mace made when Morgoth tried to hit him. Fingolfin had a sword, while Morgoth held a mace that was bigger than Fingolfin, and yet Fingolfin was able to survive being beaten to the ground by said mace.
I don't think there's anyway to depict fights on screen like that without looking a bit silly.
If you start trying to realistically depict what it would look like to fight giant humanoids, you'd end up with something that is probably very interesting to people like you and myself, but that the majority of people would find boring. Plus that's not how the source material approached combat scenes.