But at the same rate, it IS Dark Heresy, investigation is a cornerstone of the game, like looting is the D&D.
I did had in my campaigns a few characters who were combat-centric; first was a feral guardsmen sniper (he didn't talked much, since he didn't understand half the technology he saw, and the other reason is that he obeys orders, not talk like a shaman, it wasn't his place to talk and have ideas and think)
Second in my current is a guardswoman, plasmanut. She spend most of the first mission driving the car and acting as the bodyguard (of course,when combat showed up, watch out!) she pitch in in talks, but the PC, the player- pretty sure about that- and everyone in in the setting knows that the char is a combat type, and won't survive much mundane conversation at the Duke's annual ball.
That's like getting in a Call of Cthulhu game, putting everything in submachinegun, pistols, brawling, then wonder why you're bored when 85% of your game is searching for old dusty tomes in some library, or translating an ancient text from 3 dead languages and not crapping your pants.
Same with DH: you make a combat monster, don't be shocked to see that he'll be part of the scene during most if all social situation (except that old dirty dive filled with thugs with bad hygene and worse attitude)
Investigation is certainly a major part of the game, but at the same time it's not like you're gathering evidence to bring in front of a court. Certainly not without any action happening in the meantime or the constant breath of some heretical archenemy breathing down your neck wherever you go in some form or another. I think a game like this can be as action-orientated as you want it to be.
Sure, there's always something happening between 2 info gathering scenes, but that's like carrying an umbrella everyday in case it rains; can't really depends on the weather to go your way, and you're stuck hauling something that's useless to you most of the time.
While I understand the shadow over the PCs from Mr. Badguy X, he'd better have his henchmen sticking like glue to the PCs (not to mention having quite the pull+manpower+ressource) for it to be a bullet storm/melee battle/exiting chase scene at every dive bar, crummy store or market plaza.