Basically, anyone with a personality built for command, taking up the Ring, would become a tyrant of some sort. That's part of why it was so important that it came not just to hobbits, but to these hobbits, whose strongest desires were about protecting, and gardening, and living their hobbity lives. (I imagine if Lobelia Sackville-Baggins had gotten her hands on it, she wouldn't have fared so well. Not a Dark Queen by any means, but still something much more dark and dangerous than what became of Bilbo, Frodo and Sam.)
The Silmarillion was his unfinished writings. I don't recall whether he had any intention to ever publish it, but certainly, he did not make strong efforts to do so. His son Christopher had to make a monumental effort to take the various disparate scraps and versions of stories to put them together into what appears to be a coherent whole.
To say that Tolkien "intended" for Galadriel to present, in Lord of the Rings, any of the traits one would associate with a kinslaying ruthless warleader is to completely ignore the context and the manner in which he wrote those two different aspects of her.
For the record, I'm not in this camp. I think it's fair to debate whether Galadriel participated and/or was culpable in that (as other threads have).
I'm just arguing (perhaps specifically in Tolkien's case) that LotR sits inside the "legendarium" and can't be properly interpreted in a void. I don't feel that the Silmarillion stories were so unfinished that they don't reveal truths about the characters, that Tolkien must have already held when writing LotR.
But now in retrospect, I'm probably glorifying Tolkien a bit too much. It's normal for authors to change their minds about their characters, and it's normal for people reinterpreting those works to sometimes ignore those changes of mind. (It's also normal for fans to dislike those reinterpretations when it clashes with their understanding of the characters).
It's not at all unreasonable for her portrayal in the movies based on the LotR books to be...based on her portrayal in the LotR books, and not attempting to incorporate largely irrelevant details of her backstory from Tolkien's other writings.