We are in a technological age which gives us immediate access to information. MMA bouts allow us to use fighting as the starting premise to analyze what works and what doesn’t work. We can look at top rate fighters against other top rate fighters and we can a) draw inferences, b) see common denominators, c) shape theories, and, d) apply them/pressure test.
The alternative/traditional methods that apply to such arts as Wing Chun, is where we find ourselves putting a huge amount of faith into a system where there are no objective means of verifying their effectiveness. Why are we so eager to buy into myths, legends and puffs of smoke? Wing Chun does not have any decent fighters but it does have some excellent demonstrators of skill in carefully pre-planned and coached situations.
MMA provides us the (best and most morally acceptable) means to see what works and what fails at the outset. The question isn’t Wing Chun versus MMA, it is instead blind faith versus tangible results.