Plus, an argument could be made that if T’Challa hadn’t watched Killmonger choose to end his life, he might not have been swayed to set up that Wakandan outreach center in California and reveal Wakanda’s true nature to the world.
So if you think about it, for T’Challa to take that next developmental step, Killmonger needed to die.
That’s an incredibly powerful statement to go out on, and certainly in keeping with Killmonger’s characterization.
Killmonger’s ideology was twisted, but he was right about one thing: Wakanda needs to start aiding the rest of the world rather than stay isolated.