We're starting to delve into that territory where Dramatica as a tool for analysis falls apart for me, so take my comments with a grain of salt. I've never fundamentally agreed with the notion that there's a single provably objective storyform to define a movie or book. My interest in Dramatica as a means of analysis from the questions and ideas it raises, not from any belief that a measurably objective underlying storyform exists at the exclusion of all others.
With that caveat in mind...
People are always "concerned" with the future. Their fears and hopes always involve what will happen somewhere from one second to a hundred years from now. No one has ever been "concerned" with the past. When the past is referenced by a human being its always in the context of their worries about what it means for the future. Where the past is relevant to human beings it's in terms of past events being the source of conflict for things we're dealing with in the present.
So you can't really say, "Well, everyone's worried about the future so the OS concern must be the future." They're always worried about the future. That's why the question of what is the source of the conflict is so much more revealing and relevant than the question of what people think is their concern. My argument is that the source of the underlying conflict in the OS has to do not simply with a chain of past events (which is also always the case in one form or another) but rather that "Wakanda being stuck in the past creates conflicts for everyone"
No offence, and I know this has been bandied about before, but I think this is nonsense. It implies either that Dramatica is so shallow that it only concerns itself with things a ten year old can understand or that kids are somehow all geniuses and we become stupid as adults. Sometimes the nature of an underlying conflict is complex and deals with something we only really understand as adults. Think of the great and complex works of fiction you had to read in university. Now hand one to an eight year old and see if you really think they get it and adults don't.
This actually changes nothing from the initial state of the movie. We started with T'Challa in charge, we end with T'Challa in charge. Do you really think that's what the movie was about? All those themes expressed and questions raised and conflicts over what's right and wrong and the nature of one nation's responsibility to other African people's who've been oppressed, but in the end it's a movie about who gets to be king?
Events from the past are always going to be backstory in the context of the movie whether shown or not. I disagree entirely about there being "literally not conflict" when it's mentioned. M'Baku makes it clear to T'Challa that this was a failure of his father and a test of whether he's going to be a better king. T'Challa is forced to make a promise to M'Baku and his failure to live up to that promise loses him M'Baku's support and thus enables Killmonger to make a challenge for the throne.
If the vibranium theft is the first driver – and I'm not saying you're wrong – but then what is the entire opening of the movie? T'Challa and the Dora Milaje fight alongside Nakia to free women and even soldiers who are being oppressed. This was clearly meant to establish a thematic question in the story about the responsibility of a powerful African nation to aid those being oppressed by outsiders or their own people.
That's no problem, and I gave the examples. They aren't necessarily compelling to you and that's fine. As I said at the outset, I'm an outlier in this in that I don't think the type of consensus generated in a user group represents compelling evidence of a single objective storyform to the exclusion of others. In a film like Whiplash we'd probably all agree the IC is the teacher, but in Black Panther we can reasonably debate whether the IC is T'Chaka or Killmonger or Nakia or even Shuri. The process is always fuzzy at the margins.