Many of the powers are broken. Fairly weak Adeptus Arbites learns to be so commanding and awesome that everyone has to obey their orders, and they can pick a talent which makes heretics even more susceptible to those orders than loyal citizens already are. An assassin can dodge pretty much anything short of a nuclear blast multiple times per turn (and some would argue that yes, he can dodge anything, including nuclear blasts). Psykers can more or less think people out of existence with their powers (and this is a very small exagerration).