It's a really small detail in the ending of PCOV, but it's so important to me that Butters responds to his name in the end rather than pushing the Vic Chaos persona.
Butters realized growing up that something was very wrong about how he was raised and how he was hurt by his parents and his family.
Vic Chaos is a coping mechanism to distance himself from the abuse he endured as a child. His introduction solidifies that by the fact he refers to Butters as a separate individual all around. When trying to distance himself, it causes him to remain mentally the same. He's still a huge victim throughout the original timeline, especially to Cartman (shocker).
In the new timeline, where he responds to his name, he also shows he understands how shitty of a person Cartman is / was. There is no pity present. He doesn't separate himself from his past but instead heals from his past and realizes he has a lot more control of his life than he was made to believe growing up. (He also has a REAL job in this timeline!)
He's healing, even if it's juuust a little bit.