/fit/izen here. There is no such thing as a "hard" (or soft) gainer.
Your brain is utterly incapable of accurately judging how many calories you consume. Skinny people think they can eat whatever they want, and they don't gain wait. They're lying to themselves. They simply don't eat much. Fat people convince themselves that whatever they eat gets turned to fat. They're also lying to themselves. Skinny people ALWAYS consume less calories than fat people, despite what they think. Watch this.
https://www.youtube.com/watch?v=eTr1JUvEiUUSecondly, the idea of "fast" or "slow" metabolisms is also a myth. The variance of metabolic speeds between individuals of the same height and weight is so miniscule as to be inconsequential.
http://examine.com/faq/does-metabolism-vary-between-two-people.html Notice I said "same height and weight". Heavier bodies require faster metabolisms to stay alive, so fat people have faster metabolisms than skinny people (also referenced in that BBC video, above)
Bonus myth busted: somatotypes (the idea that you can be an "ectomorph" or "endomortph" or "mesomorph") is also utter bullshit.
As for a survival situation, my bet will be that a normal sized, or fit person, will outlive an overweight one. That's because the more overweight the person, the greater their risk of dying from any and all causes. In other words, a fit person and an obese person could suffer the same injury, and the obese person is more likely to die from it.
