Inner conflict does not mean corrupt.
But you said he should "learn" from Bullock, a character whose defining character trait at this point is casual brutality and contempt for anything decent. That sure sounded like you were saying you wanted Gordon to become a worse person -- not just someone struggling to live up to his ideals, but someone who "learned" to abandon his ideals.
There's certainly value in the story of a character who believes in his principles struggling to remain true to them in the face of a world that encourages abandoning them. But that doesn't mean a character needs to "learn" from a far more corrupt character. I find the very suggestion that this totally irredeemable version of Bullock is somehow more in the right than Gordon to be profoundly offensive. What the hell, exactly, are you proposing that Gordon should "learn" from this piece of scum? How to beat people up? How to torture human beings? How to stop caring altogether about the law or good police work? Bullock is the one who needs to learn from Gordon. Bad people should learn from good people.
I definitely see Gordon struggling. He's struggling with the seeming impossibility of accomplishing his goals in the face of such systematic corruption, with the difficulty of even surviving as a Gotham cop, with the seeming futility of keeping his promise to Bruce. He's definitely being challenged. If you want compromise, just putting up with Bullock's brutality is more of a moral compromise than I'm personally comfortable with, because there is never the slightest excuse for torture. But it's a compromise he's had to make just to stay alive, and it's killing him. I don't know how you can say he's not conflicted. A character can have clearly formed ideals and still have to struggle. He shouldn't have to start out as some amoral scumbag like Bullock.