While a warband of Inquisitor, Rogue Trader and Magos COULD be incredibly powerful - it could also, if well played, be very very interesting. If badly played, its very powerful - "of course the three all have exactly the same objective, or two of them follow every order given by the third...". If well played, where each character is filled out, interesting, significant in their own right, then its less powerful, and more interesting - and allows for the warband splitting, old friends becoming bitter enemies, and all the good stuff that makes Inquisitor fun.