I think the issue here is you're equating not everyone having representation equaling a small group. 200 is too many to make a decision. As you've seen in Congress and in various other worldwide institutions it can a great deal of time to get anything done. But they are also representing people on a much larger scale.
25, 50, something in between that is much more doable. But it all depends on what a council is even used for. I'm not going to say its a good decision or bad one until I know what T'Challa's idea for such a thing is in the first place.