Absolutely no one has made that argument, lol.
Even Galadriel in the books, depicted in the Second Age, was not a static character. Not exactly sure how you jumped to this conclusion for what people want to see of the character.
If you're doing a direct reply to me, my criticisms have been squarely on the lack of properly establishing a relatable character out of Galadriel. Even a simple revenge plot doesn't often undermine the main character by first introducing them having their actions questioned at every given decision. I can totally understand if you're trying to explain that there is a larger character arc at play and we'd see more of her change over the course of the series, but my point is that if they don't establish a relatable main character in the first 20 minutes of the film then it doesn't matter what character arc they present because they're losing the interest of the wider audience by frontlining this series with an unrelatable lead.
I make many comparisons to other movies that have characters bent on revenge whose stories are executed correctly by properly establishing character motives and hinting at their abilities. John Wick is a good example how to establish a character without even having to show him fight. His reputation is established through the bad guys expressing their fear of him and what he is capable of. That is enough to jump straight into the house fight scenes and really let him do his thing.
That's all we needed for Galadriel's character. Preferrably in a way that also shows off her leadership skills, not just how well she carries the team.
As for making this character a completely new one, I think that would have been a better option since it adds some stakes and tension. Being Galadriel immediately gives her plot armor because everyone knows how significant of a character she is to the story. No matter what they do to her we know she won't die, and the stakes wouldn't be the same as if it were a completely new character. I think that's what worked better for Arondir than with Galadriel. Even though she was facing bigger stakes, I never felt like she was ever at risk knowing what they have in store for her. With Arondir, it feels a lot more mysterious since we don't have any preconceptions on how the character fits the greater narrative.
It would be just as jarring if Elrond were written into the Arondir role, being the one put into a sticky situation hunting down orcs and delving into scary tunnels. It wouldn't fit his character either, and knowing it's Elrond, all of the 'jump scare' moments wouldn't be as impactful, knowing he's gonna come out of it just fine.
Despite being shown as a Herald and potential political leader, we still know he will end up taking a sword and going straight into the fight by the time of the War of the Last Alliance anyways, and it's good that they don't have to shoe-horn that into his story. His character arc doesn't need to be filled with life-threatening situations just to keep the show interesting. I'm not quite sure why they think it appropriate for Galadriel.