The problem is that Ken has about 6 statements to put him above Kasumi, from guides and the series, but they were made before Souten no Ken was released.
On the other hand, if you go and compare Kasumi and Ken on some things, Kasumi is just better, for instance: fighting against people with shifted tsubos, Ken almost got killed, Kasumi found a counter immediately; fighting against chi/life drain, Ken almost died, Kasumi found a counter in 2 seconds, add to this the fact that Kasumi is stated to be "the strongest man of Hokuto" in REGENESIS and I think it's pretty clear that they are about to retcon Kasumi into being comparable if not better than Ken