But looking at it strictly from a military/political perspective this makes no sense. If you are a Merc and you are a double agent you are signed on for some pretty deep **** so you better be ready for some tricky fall out which may include torture to people you love and or even their death. It is all about loyalties at the core of who you are and at the end of the day who and what you stand for. The Recruit ....anyone??
The day he signed on with the Inquisition (took a new job and was getting paid for it) he agreed to feed them information and that made him a double agent at that point.
By exposing that....(saving the Chargers so you can keep Bull happy) that blows Bull's cover and essentially puts him at greater risk actually.
The point is....the way it plays out in the end if you sacrifice the Chargers....Bull was NEVER loyal to you period. The Chargers choice just happen to be the means to the end (points in the game to trigger the betrayal scene) and so it's like Whoa? What? you mean all that stuff we did the beers, the dragon killing the banter...all that was just a lie? That is how it comes off if you get the betrayal...that he was doing it from the start. So the Chargers decision in the end didn't make him betray you. If we could ask Bull if that is what did it he probably would say...nah... I was a jerk all along...that was just the icing on the cake. I think that is what the OP was trying to say....can the Bull character really be trusted at all?
Hope that makes sense.
But it does it makes perfect sense actually.
You are not Bull's Superior if you save the dreadnought. The Qun is. And the Qun told him to stab you in the back and so he did. You saving the dreadnought reaffirms Bull's belief that the Qun should come first. And so he puts it first. Even over the Inquisitor.
And yeah those loyalties of his...to the QUN. Bull is never loyal to you until save the Chargers. That's when you tell him it's okay to be disloyal to the Qun it doesn't make him mad (his greatest fear is madness). It doesn't make him a beast. The Tal Vashoth he killed were most likely not mindless beast either. You tell him all this in the post saving Chargers conversation.
I don't think you get that Bull was a spy for the Qunari. He is not the Inquisitor's spy. Bull wasn't a double agent til Trespasser he wasn't working against the Qun in base Inquisition.
There is no cover to be blown. Bull told you what he was from the start. Literally it's one of the first "I'm a spy" related line he has. I just recruited him not even 2 minutes ago. He was put in place to be close to you so the Qunari could exploit that. And they do if he remains loyal to them.
Yes. Bull was never loyal to you if you kept him in the Qun. That's the running message with Qunari is that they're fair weather friends and will stab you in the back as soon as their Qun demands. You gain Bull's loyalty by breaking him from the Qun.
The chargers design is part of him being tied to the Qun. If Bull is a Qunari he's going to betray you because the Qun demands you be betrayed for the greater good.
As for trusting Bull's character not if you leave Bull Qunari? You can't trust him worth a damn. That's why his Qunari name means liar. Getting him away from that means yeah you can trust him (he's still a liar though because it's ingrained in him at that point but it's not stab you in the back lies).