This is garbage.
The juxtaposition of the character’s derogatory name, “Nigger Jim”, with his absolutely saintly character, gives the book punch. Twain was a masterful writer; these morons want to emasculate him.
"The people whom Huck and Jim encounter on the Mississippi are drunkards, murderers, bullies, swindlers, lynchers, thieves, liars, mows, frauds, child abusers, numbskulls, hypocrites, windbags and traders in human flesh. All are white. The one man of honor in this phantasmagoria is 'Nigger Jim,' as Twain called him to emphasize the irony of a society in which the only true gentleman was held beneath contempt."
You are absolutely right.
Huck Finn is one of the most powerful anti-racism statements ever written.
I found the end, where Huck decides to help Jim escape and just accepts this means he will go to hell, profoundly moving.
Particularly when you remember the author was raised to believe exactly the same thing and had obviously rejected it.
Those who cannot see this and instead fixate on the use of particular words are idiots.