mostly diet, but genetics make it impossible to figure out. At my gym there's a guy who works out every day hard and his cheat meals are maybe as bad as my good meals. He looks in good shape. His friend works out about half as much and eats California Burritos almost every damn day (steak + fries + cheese) from a place where they're the size of a small arm. And he's ripped, you can which one works out harder and eats better. But it's damn close considering how the 2nd one has basically the worst diet you could imagine.
It is A LOT easier for some guys to get a 6 pack than others.
It isn't impossible to figure it out. The guy who works out everyday should probably rest a bit more. No point training everyday unless he has specific goals. Does he squat or deadlift? Does he do hard ab exercises for say 6-10reps and not loads of crunches over and over again?
The guy who is eating burritos is getting more rest and burritos aren't too bad, it depends on what the rest of his diet is like. Matt Ogus eats like 1-2 burritos everyday. Some guys can cut on 200-250g of carbs and others can't. I know I can't
Out of the 2 which of them is stronger?
It's like this guy at my bros place of work. He works out a lot but we aren't sure what he actually does in the gym. Says he is in the same shape as my bro. They play at the company 7's tournament and no one can believe the shape that my bro is in. The other guy is no where near my bros shape. He looks moderately built but not built and has a bit of a gut. Not even a flat stomach.
Some guys get a 6 pack at 8% and others at 14%. It depends on how built your abs are. The more built they are the higher a % you can get away with.
Diet is 90% to show a 6 pack but if you have NO AB DEVELOPMENT you are f0cked.
Koing