Remember, the game bases its balance mostly on physics, using joules, muzzle energy, etc to produce the performance of a given platform.
SCAR-H with it's shorter barrel than the M14 will have less muzzle energy and because of it, it will have less joules on impact meaning less damage and less penetration too, it has a shorter barrel so it makes it more wieldy in closer quarters, it has controls that allow it to be more user friendly and do quicker reloads and such, another point of note when it comes to supply cost.
G3 has a longer barrel than the SCAR so it gets more velocity and thus more joules on impact but has less user-friendly controls, so it has more potent performance with less practical things punishing it when it comes to reloads and such.
All this also plays into penetration of the rounds, what they can go through and what will stop it based on how fast the round is going etc.
5.56x45mm/.223 is fast but can be stopped, not the same potency as a 7.62x51mm or .308, or for that matter 7.62x54R.. it doesn't have the same weight to it so it won't hit that hard, but because of it that means it doesn't need as much powder ignited to get it up to speeds meaning that it will also have less recoil due to less explosive force from the expanding propellant gasses required.
Kinetic energy from a 5.56 projectile moving close to the same speed as a 7.62 projectile is about 2/3rds, a number vastly lower in terms of direct energy delivery on target, and the larger projectile of the 7.62 would also have better hydrostatic displacement and expansion on flesh.
All that being said, there is the point of note to be mentioned, that I wish they would put the "long barrel" option back into the game.. so players can choose to spend more supply points on getting more velocity but losing weapon mobility while they're at it (but it should cost more than the 1 supply it did previously, it should at least be 2 supply minimum, but would also be nice if there was a short-barrel option as well... but that's a topic for a separate thread).
The SCAR is about 85m/s slower velocity than a G3, and I think about 140m/s lower than the M14 EBR if I'm not mistaken.. so the SCAR will not carry the same energy on target, it just simply won't. Don't complain about weapon damage if you don't understand why the devs have done it as they have, just because you're used to how other games have used arbitrary numbers (like call of duty and battlefield).
The devs have done a good job with the reasoning for why individual guns perform (damage-wise and penetration-wise) as they do.
Please don't complain if you haven't even read what the weapon-stats say on each weapon's stats, that's on the right side of the screen as you pick them and alter their performance via attachment etc.