Considered more efficient at burning fat would be a better description. Being dual fuel is spectrum - some better at burning fat, some not.

-Some fat adaptation, meaning better than the couch potato, happens in active people/endurance based people.

-More fat adaptation occurs when athletes train in carb depleted states.

-True fat adaptation doesn't really occur for 2-3-4++ months of being in complete ketosis.

We need to see a chart like the one you posted where the subjects are truly fat adapted athletes. I'm not talking using subjects that are two weeks into ketosis - which many of the studies out there are based on - I'm talkin long term, well trained "keto" type athletes.

I suspect there would be a shift in the fuel changeover points.

I know for me personally - 6+ years fat adapted, but not an athlete - I can go into mid Z3/tempo range for 2+ hours on a day where I didn't consume any extra carbs and only consume about 20+/- per hour to keep the blood glucose topped off. Blood glucose and muscle glucose are two different systems - if BG's dip, you can feel like you are bonking - but still have plenty in the muscle "tank".

Again, personally - I don't "blow up" until I hit prolonged bouts of sweet spot or above. Or if I push into Z4/Z5 too often on longer efforts, like a century.

Just for clarity - I am not saying that fat is a superior energy source for bike racers. It's not.