I've heard on numerous occasions that Kickboxing (Muay Thai) is the most effective form of martial art.
That type of statement tends to aggrivate people who practice more complex and technical martial arts such as Karate, Judo or Kung fu.
Case in point ( albiet very generalised ) , some time ago a group of Karate blackbelts, Judo masters and Kung fu experts travelled to Thailand to challenge the various Muay Thai champions. In every bout the Kickboxer was able to KO the non kickboxing opponent.
Two years later and still bitter about their loses and the notion that Muay Thai is the most effective art, the various Karate, Judo and Kung fu experts returned to Thailand to once again challenge the Muay Thai fighters.
End result - the non kickboxing fighters were KO'ed again.
Most likely this is because Kickboxing is simple and brutal. Muay Thai fighters generally start at a young age and become accustomed to being beaten to a pulp. Whereas when a Karate blackbelt takes a kick to the head from a Muay Thai fighter, they are unable to cope with the blow and tend to be KO'ed.
Also it doesn't take a ridiculous amount of time to become proficient in Kickboxing as opposed to the time required to become a Karate blackbelt.
And I'll never forget Adam Watt (former 3 time world kickboxing champion) telling me that when kicked in the groin to just grin and bear it......