Personally I do think they did a really good job with Killmonger and how he managed to play the right cards to get exactly what he wanted.
He saved Tony’s life and immediately become in his good graces and outed Obadiah, which solidified that status of a trustworthy and resourceful ally. He then bonded with Tony and since they were similar people the bond grew bigger, they developed the drones together…
Later on they were both on board with getting the vibranium. Killmonger played both sides in the negotation, planed with Klaw and came in late to take Black Panther and Rodey out, while making it seem like they took each other out.
Of course Iron Man then saw through it with the help of Jarvis, since it became personal he wanted revenge and that was basically his downfall because Tony Stark was blindsided by his own pride and Killmonger underestimated capabilities.
The proof of any wrong doing was basically erased by Killmonger. Without proof and the backing of the military because of his war hero status, he still managed to progress his plan. The military came in and took everything single thing from Tony which basically meant that Pepper lost any real means or influence in the bigger picture.
Next step was ambushing Klaw and delivering him as a trophy which worked out as a way of solidifying his approach to Wakanda, coupled with the fact that Killmonger was part of them and basically royal family. He then played a card in form of being an informer for the upcoming attack and last but not least the battle hero card, his actions gave him even more cred with the royal family and the Wakandans. One thing led to another and he naturally became the Black Panther.
Killmonger was cunning, he forced himself to the scene as a savior, gained trust and influence, made use of his abilities, played the cards right and filled a vacuum that he himself created.
Of course from the audience perspective and knowing what we know it’s easier to label him and his actions. On the ground it was Pepper who seem to mistrust him and Shuri who used her genius ability to uncover the truth.
