We technically do. Some people just decide to ignore every difference except a few particular ones, like very strongly diverging skin tones. There is no such thing as a strict, distinct "white race", or "black race" scientifically speaking. There's just very large catalogs of certain gene markers, a lot of which can be WILDLY different even within families, while other may be similar even across global distances. Humans just pick out some traits and say "these are important!" for no real reason other than that they want that to be the case. Race is a construct, not because "herp derp the left is trying to tell us skin color isn't real don't they have eyes", but because you choose certain criteria and make them more important than others based on nothing but cultural and traditional biases.
None of that matters for a world where evolution wasn't a thing anyway, because the canon lore is that some gods just came along and went "hocus pocus, let there be dwarves/elves/humans/whatever".
But to get back to the actual show instead of more derailing...
The problem is, Tolkien's source material is in itself very diverse. There's cohesive titles like the Hobbit or the Lord of the Rings, but even something like the Silmarillion is more of a collection of things. And then there's the myriad other short snippets, drafts, appendices, letters, and whatnot through which Tolkien developed his world over long periods of time. Very often changing things as time went by, sometimes quite substantially.
Galadriel is such an example. He said himself in his letters that his goal was to make her a very different character, much more of a woman-warrior type than the composed ruler figure we see in LotR. And she always had sass - one of her most famous appearances in the Simarillion has her give the metaphorical finger to THE greatest elf who ever lived. Three times. She was a rebel. She joined with the Noldor in their resistance against the Valar. It's not against her character at all to be going against Gil-galad in the show, and having her own, stubborn way of things. ESPECIALLY considering the plans Tolkien had for her that he simply didn't get around to realizing before his death (but did speak about in his letters).
Her holding a grudge for a bunch of centuries is similarly entirely in line with elves of the First and Second Age. The whole reason so many of them left Aman was exactly that: an unquenchable grudge that drove them to rampaging and often self-destructive violence. That's a core tenet of the entire narrative of elves in Middle Earth, and it makes perfect sense that Galadriel in the show would embody that.
That's not to say there isn't any avenue for criticism here. If anything, my problem, personally, lies not with Galadriel's motivation or role in the narrative, but with the way her actress puts it on the screen. It's what creates the "bitchy" image in people's heads, because she doesn't quite manage to properly convey the depth of emotion that the character has to contest with inside herself: her desire to be of service to her people, while at the same time unable to let go of the grudge against her brother's killers (which is effectively a stand-in for the Oath of Fëanor from the Silmarillion that they're not allowed to touch in the show). The problem, to me, is that this emotional ambiguity needs to be tempered by the fact that unlike her actress, Galadriel isn't in her 30s. She's THOUSANDS of years old. She has internalized those emotions for longer than most of the human race has been alive. That requires and creates a complexity of character you can't just brush over with the same strokes you use to portray a random 30-something in a generic, non-fantasy drama. It makes her come across as immature and obstinate, when that is absolutely NOT what Galadriel is about. And that's the fault of the director and the actress both. It's their job to plumb such particulars when it comes to a complicated role like that, and work on making that kind of portrayal convincing. Instead, it seems they were trying to go for some kind of pseudo-Daenerys to please executives, and that is just so, so, so not the way to go.