The idea is to avoid the ground in the first place. Fighting on the ground with one person can mean getting hit by everyone else still on their feet. Wing Chun doesn't try to fight force wastefully. If the opponent has more power, pushing against it will only dissipate your own energy. We stick to the opponent and find their line of force and use that same line against them. The unaware opponent that doesn't change quickly enough will have their force used against them.
If someone tries to grab you, adjust quickly and use that power to attack again. If they do grab you, use a change of direction that they do not expect to break loose and attack simultaneously. This is where practice and sensitivity come together. Ideally, avoid being grabbed and meeting the ground. Be more skilled to overcome the tactics of the other side.