I think there is a balance.
I have never seen a KPOP group with all visuals who can't sing, dance, or do anything.
If you are pretty enough, I think you will make the group regardless as long as you can dance or learn to dance. You don't have to be a great dancer, but at least be able to keep up with the group. They will find a position for you. This is for TRUE visuals though. Like Tzuyu, Suzy, Seolhyun, Yoona, Jisoo, Wonyoung, etc type visuals. You cannot just be pretty and think you are going to make it.
But, a whole group cannot survive on that alone. They need at least some members who can sing, dance, and have great stage presence, and for that particular position your attractive level does not have to be visual level. You just have to be attractive enough to look at and be found visually appealing.
I think there are way more talented average looking idols with good styling versus visual members with the bare minimum talent. But even average looking idols have to have certain physical proportions to make the cut.