It is less anger management than learning to hold an impulse without acting on it. That is a skill, and skills can be learned in a way that characters cannot.

What the research says

In a randomised controlled trial with forensic mental health patients, anger management based on acceptance and commitment therapy reduced anger rumination and impulsivity scores. Training what happens after the impulse, rather than the anger itself, has some support behind it. It was a particular setting with a particular group, and programmes of this kind generally show modest rather than dramatic effects.

Strength of evidence: one line of research. A single study, or a theoretical account.