If you don’t think the techniques of kung-fu can work in a cage (at the highest level), think again.
Some kung-fu techniques cannot be used inside the cage, due to the ruleset, but there are still plenty which can and already are being put to use! Kung-fu is considered the root of all martial arts, if you train for performance, your kung-fu will only be good for performance. If you train for fighting inside a cage (with plenty of place to move, against trained strategic martial artists), you will be able to use your kung-fu inside the cage (example: Cung Le who trained sanda and competed in wushu competitions before MMA). If you train for self defense (attacks from the back, multiple opponents, improvised weapons, agressive thugs) you will hone and adapt your kung-fu for those scenarios.
No martial arts purpose is greater than any other.
Some styles lend themselves more to one purpose than others (capoeira is easier to impress an audience with than krav maga, while krav maga is easier to use for self defense) but what matters most is not what you train but how.