There are different organizations. In the early Kickboxing days, the guy who knew boxing just got the karate/kickboxer into a corner and Koed him. There were also two rival org, one with low kicks allowed.
If the Kyokushin team knocked out two out of three Muay Thai fighters with punches to the face.. How on earth would they manage a world class boxer, supposing the boxer conditions his legs for low kicks 6 months in advance?
Maybe today is different, but my money back in those days would be on the boxer to KO them.