Ok, hear me out on this one before you cry foul! :-)
I find adamantium faith extremely binary. Either you have it or you dont. Meaning either you roll pinning/fear tests or you dont. One day you may run away afraid of a some demon minion. The next day you are ready to face the greatest demon lord in existence. In my opinion this talents makes too much of a difference between having it and not having it.
In the adventure modules both in Haarlock series and the Apostasy Gambit series there are some talents where fear levels get reduced by a factor of 1.
Why not capitalize on that idea? It could be a talent called "Fearless" that can be learned multiple times to reduce fear levels. So if you have fearless II you only roll fear check if you meet a foe with fear aura 3 or more and then you even get +20 on the roll (you reduce the level by 2). That is a pretty nice talent just for that. The requirements for taking higher ranks of fearless could be higher willpower (and having the previous rank of course).
With regards to pinning, you could reintroduce Nerves of Steel as a tier 1 or 2 talent, which makes the user immune. Base it some combat aptitudes instead of willpower, as a hardened warrior should be more likely to get this for cheap that some academic/priest. It is a nice enough talent on its own.
Fear is a very important aspect of Dark Heresy. It can have huge impacts on the battles the acolytes faces. That is why I think it needs to be fleshed out a bit, and not just having this one talent that just removes this important factor from the game.
In any event, this is just an idea. :-)