Power thieves are essentially nothing but a nuisance that hit like (comparatively) wet noodles in 1v1 scenarios. Sure they can gank and backstab you for high crits when you're distracted with something else, but they're poor duelists. More often then not, they are forced to run away. After the balance patch this will be exacerbated. Conditions will like reign supreme and trailblazer mirages will have high success.