I don't know enough Wing Chun (yet) to make an educated statement based on my own opinion, but I can say that martial artists saying their style is the "best" is not a Wing Chun exclusive. God, if I had just a penny for every TKD guy that thought TKD has it all...or some of the traditional Japanese Karate styles....and I won't mention the attitude of 80% of BJJ practitioners! LOL
About the cage....it is still sport with rules and limitations. Even the first UFC's had rules. The whole "anything goes" was just marketing. No biting, small joint manipulations, no eye gouging...ect. Granted, they were few but they were still there...and I am not saying it hindered Wing Chun as before I said I am too new at it. I have trained in Koeikan Karate, TKD, MMA/Grappling, and tried a few other styles. Some have a well rounded curriculum but none master all. It's the fighter not the label on his training.