He is needed, for the story Black Panther is telling. You’re shifting your criticism away from the way it’s connected to just a concern with the script of Black Panther.
So to that concern, we saw very little of T’Chaka. I can’t really defend or criticize his effectiveness. Maybe that’s poor storytelling that we’re only told of his history with Klaue instead of being shown.
But where we go from there with Killmonger, T’Challa, and Klaue, all makes perfect sense in the context of Black Panther. T’Challa is able to apprehend Klaue, although Klaue certainly puts up a fight. Klaue is shown as capable, but not untouchable, and T’Challa only looses Klaue because he’s trying to make an attempt at doing this the right way without making an enemy of the CIA. Whether Killmonger specifically meant to let Klaue get briefly captured or not, working with him is what gets him close enough that he can make his move and take out Klaue when he’s ready to go to Wakanda.
So again, to your point about the forced connections in the greater MCU, sure, but that wasn’t the problem in Black Panther. You’ve got a much stronger case that Klaue should’ve been cut from AoU (there was a lot wrong with that movie), but I’m standing my ground on Black Panther—it’s one of the least beholden to the other MCU movies.
And to reiterate for @tomchick, Klaue Klaue Klaue, Killmonger Killmonger Klaue Killmonger Klaue Klaue.