For example I do not accept this , so your statement "accepted by everyone" is wrong. Sorry.
It is questioned (for example) on this martial arts forum. Your statement "is not to be questioned" is wrong again.
And yes: STATEMENT NEEDS PROOF.
Being the best fighter among failures is not huge achievement.
One good fighter from a style means nothing. 100 good fighters from a style means something. BJJ is proven not because of Royce and first UFCs, but because of thousands other fighters who used succesfully BJJ in fights. The same wrestling, boxing, judo, sambo etc.
Wrestling and kyokushin have different mentality, too. Wrestling and boxing have different mentality, BJJ and Muai Thain have different mentality but there are thousands fighters who succesfully mixed them.
Sticking with one (especially as limited as Wing Chun) style is straight path to defeat.