Kongo doesn't have great technique on his kicks and his boxing leaves a lot to be desired. He does have good power and I assume he had a good Thai clinch but he never uses it in the octagon and he was accomplished in Muay Thai, not K1 style kickboxing.
He has great kicks in his kickboxing fights, and yes his clinch is good too. His titles and video don't lie. His problem in the octagon is fear of TD's suppressing his kicks against all but purist strikers and lack of defense vs punchers... and the fact that a good clinch means something totally different when you're clinching with a powerful wrestler who wants to put you on your back. You really should just read the article. Slack is a very astute striking analyst.
Everybody good, plenty of slaves for my robot colony?