CICO (calories in vs calories out) is a nutritional myth. 400 grams of carbs is a lot different metabolically than 400 grams of protein, not the least which reason being the thermogenic effect of protein digestion -- protein digestion requires energy and produces heat. Anyone who has ever experienced the "meat sweats" will vouch for this fact.
I've had athletes on a *SEVERE* calorie restriction for 6 days a week, with continued training for their sport, followed by a massive overfeed on the 7th day, gain some serious muscle while getting shredded in less than 10 weeks.
I can take *any* able-bodied person with a bodyfat below 30% and make them look like they're a professional athlete in 12 weeks or less if they follow *every single thing I say* without exception, and this is without gear. With gear? 8-10 weeks.
My point in all this is not to brag, it's to show how powerful the manipulation of metabolic adaptations through diet and exercise can be. There is no able-bodied person that cannot transform, quickly, if they just understand how and why the body adapts to various stressors.