I tend to think of FitD as a sort of funhouse mirror version of PbtA- they've got similar intents and toolkits, but lots of little details in how they implement them that give a different feel that designers and players can take advantage of and some big higher-level changes (like Moves v breaking rolls into effect and positioning, the introduction of the Stress economy, whether or not you bake downtimes into the structure of play) that produce very different feels in motion.