Villains, by definition, are generally ruthless. It's rather difficult to be a villain in a genre such as wuxia fiction without a strong measure of ruthless.
Which wuxia *heroes*, however, are also known for being ruthless? These are characters who are basically good and decent, and who serve the cause of order and justice, but whose methods against those whom they deem to be evil can be just as ruthless as those of any villain.
I don't count Wai Siu Bo because he was no hero (protagonist, yes, but not a hero), but in Jin Yong's canon, I can't identify any ruthless heroic characters. Gu Long, however, has a few: Sai Mun Chui Sheut, though acknowledged by wulin as a hero, was utterly ruthless towards his enemies. Ding Pang, Ah Fei, and to a lesser extent, Lee Chum Foon could also be quite ruthless.