You're right that it's easy to out-eat the running you can sustain as a regularly fit person, but there's no "only" about 2000 calories

2000 calories is pretty near the daily calory requirement for a healthy weight human. If you are of healthy weight and eat appropriately, you pretty much have to eat twice as much to compensate for that marathon

If you burn 2k calories daily exercising you are no longer gen pop. The case still stands, statistically nobody is out-exercising a bad diet.

For fatties the benefit is even greater