"Nuanced discussions" is more about describing a design to a model, asking the model to critique your design and ask you for clarifications, and then you providing those clarifications and the model "getting it" and proceeding to additional levels of detail before implementation. In particular the models being able to highlight concerns you have not yet thought about is a pretty good sign of this. Fable is noticeably better at this compared to Opus.

I was not talking about models making mistakes. Mistakes, and then models making up justifications for those mistakes, is a failure mode of any LLM, and Fable is no different in that regard. Newer models might make less mistakes, or at least make less egregious mistakes, but they still make mistakes.