In order to have good structure/rooting, one needs to develop "body vibration force". When a force is applied on your body, your body will absorb it first (soft). Your body then bounce that force back (hard). The day that your body can change from soft to hard and then back to soft, you will have good structure/rooting.The problem with soft-only arts is that they cannot practice what they preach.
If you only have soft force and don't have hard force, you don't have "body vibration force".
Example of "body vibration force".