I'm not trying to say a villain like Eric Killmonger could be talked down with diplomacy. I am trying to say that T'Challa doesn't attack Killmonger's assumptions, leaving the audience with some sort of nebulous sense that Killmonger was basically right, just not the right man for the job, rather than being fundamentally wrong about almost everything.
I certainly got the impression the Director was pretty sympathetic to Killmonger's 'Black Hitler' position - but I also thought that this sympathetic portrayal was what made him a powerful villain, as opposed to the usual Hollywood Nazi stereotypes. You see the same effect with Magneto sometimes.