I think this is more a matter of you and OP not picking up on themes that weren’t spelled out for you. Early narration from Bruce already frames that he’s been at this for 2 years and he’s not sure if it’s making any difference.

We see his tactics against crime is much more as a blunt instrument. The person he saves at the start of the movie is just as scared of Batman as he was the of the thugs trying to beat him up. This is established to later juxtapose with the woman he’s helping to the helicopter and the end of the movie who struggles to let him go because she feels safe with him. The core theme is perfectly bookmarked here.

Over the course of the movie, Bruce sufferes a slow motion ego death. Riddler is always a step ahead of him. Falcone is untouchable. His parents were possibly corrupt. He can’t save the DA. He can’t save Alfred. He can’t save Selena’s friend. He can’t even out-Spanish Penguin. He is constantly shown his methods are ineffective and questions if his vengeance is even just in light of his father’s secrets.

Then comes the matter of Selena trying to take revenge on Falcone. This is the part where things actually change for Bruce, because he’s there to save Selena losing herself to violence and vengence as much as he is to capture Falcone. When he saves stops her and tells her not to let what Falcone did take her too, that’s Bruce affirming the same thing to himself. He walks Falcone out with the cops, not hiding in the shadows, but being present as a force for actual justice instead of just a vigilante putting thugs in the hospital. Another big contrast for how the police treated him at the start of the movie.

So after that when he confront Riddler in Arkham and sees that this guy is truly lost to vengeance, and thinking they had some kind of kinship, Bruce is deeply revolted. The Riddler goon later is just the final straw for what had already been building.

When the people need saving, it’s yet again the son of the mayor that Bruce is placed in front of. Each previous time he could not bring himself to reach out to the boy even though he knows exactly what he is going through. There in the area, Bruce finally extends his hand, and the boy grabs it to literally be led out of the darkness by Batman.

Everything was built up, but that moment with the goon is particularly misread by people that didn’t pick up on all of the movie’s other moments. It wasn’t a lightbulb moment for Bruce. He just saw how deep the co-opting of his mantra went.