I played a lot of Inquisitor for a time, and it varies so greatly. It is true that an inquisitor, in general, will almost always have their arse handed to them on a plate within a very short space of time when pitted against a space marine - even with an entourage.
But that means pretty much nothing. A space marine is completely useless in that setting except when killing everything that moves. If your intent is not to literally make a space marine appear and then for everything else to die immediately, then a space marine is completely useless to you and you're not going to get very far at all. An inquisitor is just a completely different type of character that isn't there purely as a killing machine.
Aside from that, anyone who ever played with any official rules for assassins in Inquisitor (eversor assassin especially) will know that they are another level above the disparity still: An eversor was so ridiculously capable of chopping up everything that walks (even space marines) that it wasn't eligible as a PC.
It's versatility and character that made the inquisitor really useful. They could be exceptionally hard, be tough to kill, have loads of awesome equipment, and have an array of good psychic powers - and yet still manage not to suffer any particularly onerous personality defects that would prevent them from investigation, enforcing their authority, or otherwise continuing with their endeavours. A space marine on the other hand wouldn't get you anywhere. You can't just walk into a bar and blend in. You can't just mingle with noble born aristocrats in order to infiltrate some sort of cult. ALL you can do with it is step out, kill all moving things, and then praise the emperor for a bit. They really are useless.
All of this has happened before.
Last edited by Baltar; 08-16-12 at 08:08 AM.