For people saying Killmongers "reign on the top was short like lepprecons", it was to be expected in this movie.
Maybe the save Killmonger for the sequel and maybe they make Klaw the main villian. But that would have defeated the purpose of the theme which was...
T'chaka and former kings were willing go to extremes to keep wakanda isolated including lying, killing and abandoning thier own blood.
Some Wakandans were fed up of hiding and Killmonger was a byproduct of the leadership's lies and neglect. Killmonger wasn't just out for revenge because his uncle killed his father. He was more angry at wakanda letting black people around the world be oppressed.
They were around during slavery and instead of driving colonialism and the slave trade out of Africa, they sat back and did nothing which is more egregious. That's something Killmongers dad resented.
Also, T'chala didn't have to fight Killmonger for the crown. I think part of him did it out of Guilt. I think he felt that everything he looked up to in his father was tainted and in turn his legacy was tainted as well. Mentally he wasn't prepared and thus he lost before the first blow was struck.