In a weird way it does the same thing stopping power did in MW2. It's kinda brilliant actually.
Apart from being very useful and cheap at the same time, it makes you think about picking Ghost. Wanna be stealthy? You're gonna get blown behind every corner and every time you stop to reload. Hence the importance of flak jacket.
Yeah you can go with the flak jacket/ghost route but that's the noob combo. You're not gonna be as efficient as if you paired it with hardline, lightweight or simply picked additional perk from a different tier.