It's a matter of skill.
The fact is people who use the ACR, MP7, and Striker every game don't have as much skill.
ACR is a no-recoil assault rifle which makes it excellent at range as well as having a decent RoF for close quarter combat.
MP7 is an SMG with no recoil which means you can use it at assault rifle range.
Striker has extremely good range for a shotty and a fast RoF compared to pumps.
Other weapons take a lot of limiting engagements, specific perk selections, changes in style, and compensating for recoil. These weapons don't. That's why kids use them.
Funny thing is these weapons are outclassed by other weapons easily. Striker will lose to a pump or AA12 in very close quarters if used correctly, MP7 has a slower time to kill than all other SMG's except for maybe the MP5, and the ACR is inferior in CQC to the M4 and G36 at least, inferior at mid range to the AK at least, and inferior at long range to probably the MK and M16.
So the weapons are well-balanced. But kids who have easy weapons on every class are terrible at the game. You're right- if the easy wepaons were removed or nerfed, these kid's K/D's would probably plummet. They don't know how to adapt to using weapons otherwise they'd be using them to begin.
