Abit I'm not sure that Kao is one of the top in all of SW, sure his one showing was great and he is a Battlemaster and he did fight Malgus and Vindican, sure would he be one of the top of his era? Yes of course. But I'm not sure that single showing, would elevate him up to the Top 10 in all of Star Wars.
There are A LOT of duelists in the galaxy to look over after all.