Thanks for sharing. Agree with your observation that Killmonger's reign as king would have likely been short.
I thought W'kabi's story arc was quite believable. He trusted his King to deliver him justice and when T'challa came back without Klaue he naturally felt disappointed and to a certain extent betrayed. So when Killmonger comes in and shows Klaue's body to W'kabi, I feel it is understandable that W'kabi backed him as leader as he delivered justice for him.
And that M'Buku challenged for the Wakanda kingdom, lost, and latter came to T'Challa's rescue was a nice twist.
That Black Panther could incorporate to twists -- two characters switch sides -- allowed the film to breathe. In other words, it allowed characters to have a depth and sense of life.