It’s really a case of the rich getting richer when it comes to exercise, because if you’re fitter you can sustain a calorie burn rate far higher than someone who isn’t.

On my bike I have a power meter which uses strain guages and an accelerometer to calculate force x distance / time at the crankset so I have accurate calorie burn numbers.

Riding for an hour at the output a generally sedentary person can manage, I’ll burn sub 500 calories. Riding at my maximum output for an hour burns about 1000. Given that the recommended energy intake for a day is 2500, you can see what a difference that makes proportionally to what you can consume.

Indeed, energy intake is a big part of the equation and indeed a single run/exercise will not burn off a gigantic amount of calories. What repeated exercise does do is to raise your metabolism and increase muscle mass which will increase energy consumption at rest and combat all kinds of other symptoms.