I don't get this thing of everyone having to be a great dancer for them to be a strong dance group, because that is not true.
For example, After School are probably considered the best female group in terms of choreo, and yet Raina is a pretty weak dancer. However she manages to follow the choreo decently enough to keep the group's performances looking polished. And while you will expect a few members to slay with their dancing, this is more than enough for the other members who are vocalists etc.
What you need in a group is a good balance, which entails a blend of vocals, rapping, visuals and general star quality. Unless you're aiming for having the most talented and well-rounded group in K-Pop, a group consisting completely of dancers is going to suffer severely in other equally important aspects.