I'm so sorry that you're having to deal with this. Truly, I don't think you had a choice. You had your vet advising you based on Christofur's condition at the time, and the former owners were to blame for any lack of information. And really, if the only option was to keep the poor little guy heavily medicated, what kind of life would that have been?

You did your very best for a very ill kitty, and that's all that can be asked of any of us.