It's dynamic down scaling. Your damage is adjusted depending on the level of the enemy. Let's be honest after a while of one shot killing enemies wouldn't it get boring ? IMO the scaling seems to be spot on, you're not underpowered and you're not overpowered. You seem to be evenly matched in terms of damage. When playing co-op this is even more important. Take this for example : You're in patrol with a player fresh to the game. He's level 3 and you're level 20. There's a few level 2 dregs shooting at him and he's shooting back. You come in and one hit kill everything. Is that fun to the new player ?