Any negative language we use to describe a creature will have, unfortunately, been used to describe a certain group of people, to make them non-human. Fear and dehumanization of the other has unfortunately always been with us and probably always will be.
I agree that some of the language should be fixed, but there will always be people who see correlations.
Yes, the language should definitely be fixed.
This reminds me of the "everything purple" argument. Eventually, you run out of correlating humanoid factors that can be evil. It's all about how far can you diverge from real life history and have it be acceptable with everyone. Can someone make a dark skinned evil race? For some, if they give them one eye, a giant mouth, a horn, goat legs, and four arms, it is acceptable. For others, all it takes is white hair and red eyes. That's where purple comes in. If it is purple, since it has not real life connection, then it can be evil.
But that leads to language...
And that is your original point. Language is finite. All that happens is people run the same litmus test on language that they do with visual art. So the author must mix and match different negative language through history in order to pass the litmus. But no matter how it is done, you are correct, there will always be allusions to some writing in history. It is how much it mirrors a specific group that causes conflict.
Maybe there best bet is to have the races as stand alone proxies in the PHB. No description. Then describe places PC's can come from, and use those for the traits and abilities and skills. So everyplace is a mixture of dwarves, elves, tieflings, half-orcs, etc. It'll just be the culture they come from that determines what they get. Then you can go all out and have a crazy cannibalistic, militant, slave holding society and it doesn't matter - because all the races partake in it.