They were both right and wrong.
Killmonger was right about Wakanda being shady for having resources but, allowing blacks worldwide to fend for themselves. But he was wrong because he was a tyrant in the making. He was a charismatic character, his story was sad and most of his ideas made sense. But he would've been a terrible King because he was too hateful and bitter.
T'Challa was wrong to continue the traditions of the past in the world where the threats were no longer as great. He corrected that by adopting some of the views that Killmonger shared. Despite being wrong at first, when its all said and done, he would make a better king than Killmonger in the long run.
Also, the previous Panthers weren't wrong for isolating Wakanda. It was the right move
at the time as Europeans would have done everything in their power to plunder the country. But by the time T'Chaka came to power, colonialism had died down. It wasn't the 1700s or 1800s anymore. To be that fearful of being conquered that you would abandon your 10 year old nephew is foul. That was his blood and he just left him there. Didn't even as much as have somebody watch him from afar or give him a trust fund

HYON lil nikka. T'Chaka is probably the only one I can find real fault with. Everyone else is iffy for me because I can agree with them all. There's nothing black and white here. It's all shades of gray. That's why the movie is dope. And in the end, you see T'Challa goes somewhere within the middle.