I wouldn't call it a moat, but I would call it a noticeably better model. Subjectively, for my own work, I would rate the top models Fable > K3 > Sol.
But it's not like Fable is so substantially better than the other two that I would be seriously impacted if I didn't have access to it anymore. All three are amazing models, and of the three, Fable is the only one that regularly triggers refusals.
It really does depend on your application. In my domain (math research), it is substantially better. Fable can solve really hard tasks with surprising consistency. It makes mistakes, and occasionally refuses, but honestly, at the top level, ideas are the currency and the rigor is the busywork. The other models cannot come close in this domain.
If you couple Fable's idea factory with Sol's rigor, you get a real game-changer. It puts the emphasis on top-level ideas, and nearly trivialises the intermediate layers.
It's always fun to see what works for others, because for my work it'd have to be Sol > Fable. Fable makes too many mistakes.
Coordinating agents though? Fable any day.