The ritual is meant to be a formality, a tradition. Nobody actually challenges the Black Panther for rule. It's a holdover from an earlier way of life, meant to provide continuity and spirituality to a people in a time of change and transition. Especially in a culture that is as obviously concerned with it's history and it's ancestors as Wakanda.
As an example, you ever been to a wedding? Every wedding I've ever been to, they still do the whole bit with "If there be anybody who believes these two should not be wed, let them speak now or forever hold their piece" bit. It's archaic, nonsensical, and is there ever an actual objection? Of course not. But they do it anyway, because that's how it's been done for countless generations.
Now, yes, it's a problem that the Wakandan ritual has the force of law. A holdover from an older time that has been turned on those who are bound by tradition. But it's also thematic in the film. That traditions and rituals are important, culturally, but when they hold you back or open you up to exploitation or abuse they need to change. Wakanda is so bound by the way things WERE that they are no longer truly prepared for the way things ARE. And we see them struggling against those bonds, between cultural traditions and modern demands of morality and conscience, between what they have always been and what they might yet become.
I can see why it would bother somebody. But I felt it was used well in the film, thematically. The old ways coming round to haunt the more modern inhabitants, even as they must cling to them against outside forces.