Hmmmmm, is stopping power overpowered. No, Non-stopping power users have a damage multiplyer of 1. Stopping power users have a factor of 1.4. The damage scale is 35 if the damage is maxed. All shots go to the stomach with this scale. One recieves a damage bonus for an upper chest/headshot. Therefore, a gun like the ACR has something like 15-16 damage points (technically it is more) without stopping power, and 21-22 with stopping power. People start with a 100 hp. Therefore with the 15-16 it takes roughly 5-6 shots to bring someone down, with 21-22 it takes 4-5 bullets. So like stated before, Stopping Power usually takes away 1 bullet from the gun you are using. I'll repeat this, 1 bullet.
If you are complaining about stopping power, maybe you should become better at CoD. If this 1 bullet advantage makes you think Stopping Power is broken, I would say this isn't a game error. This is a user error, is it harsh? Sure. But if you're complaining because a perk causes them to kill you with 1 less bullet I have no sympathy for you. Maybe you shouldn't play. You should complain about Models Akimbo, something that truly was broken, I should know I used them.
To sum it up, complain about something that you can prove as broken. I can disprove your "stopping power is broken" with math. Sorry but you should find something else to complain about.