I think the biggest mistake is to clarify these positions too early in a group career.
Because with ou without position, there will always be these member who are more pushed as a main vocalist, the ones more pushed as a main dancer, the others moe pushe as a main rapper, the ones more pushed as face, as center etc
But It isn't always the members the fans were expecting when the official positions were announced during rookie days, the groups keep adjusting themselves for what is better for their sound and style.