There are plenty of top fighters that use their boxing 99% of the time in fights. Nogueira, Rampage, Vitor, Penn, they are all outstanding examples of how boxing can be extremely successful in MMA. Now if you only knew how to box, you would fail, but the same can be said if you obly knew how to kickbox.
Just because one fighter is a master at kickboxing, and one is a master at boxing, does not mean that the kickboxer is better.
Urijah Faber - Dustin Poirier - Demian Maia - Frankie Edgar - Georges St. Pierre - Lyoto Machida - Miesha Tate