The reason why I feel like the Wing Chun punch is sufficient for fighting is because in the way I was taught, it can be delivered from various angles. For example you can punch from your fist starting anywhere in front of your chest and shoulders, and it can land anywhere on the opponents body. This allows for a lot of variation in striking angles and targets. If you learn to connect your elbow with your hip, you can generate a lot of power this way too. It's always the same "Chong Kuen" (thrusting punch) it's just that the starting position can change horizontally from the centre line to the shoulder line or anywhere in between, and vertically from as low as the belly button to as high as the shoulder.