List the names of elite level kickboxers he fought. You can only really count the fights he had in Glory as high level and that's when he took his losses and quit kickboxing after getting KO. The rest were low level fights in China that you will never find. Pretty much what fighters consider smoker matches in muay thai/kickboxing.
Izzy is good, but people make it out like he was at the elite level in kickboxing. He just started fighting high level fighters and switched to mma/UFC when he started losing. Jan gave him trouble because of his muay thai/kickboxing background. Those are the fighters that will give him problems because Izzy's style is kickboxing, muay thai style will give him problems. Those are the type of fighters he loss to in kickboxing.