I think for any hope of real change they need a strong support structure and need to start making sustainable changes in life over time. In the case of BPD (which has been speculated with Letty) even if they seek treatment they generally don't make much progress. I don't know if that's true for all the Cluster B personalities, but BPD is, tragically, a difficult one to crack in most cases. I like to think there is always hope for even the worst of people to make some type of recovery and improvement.
At a certain age, no one cares about your childhood trauma and the "why" you are the way you are. It's hard to become an adult and break the cycle and take ownership of one's flaws and baggage.
I have to wonder if the sampling of fish in this house are a good representation of the average zoomer or just a representation of the average degenerate zoomer. I hope it's the latter.