Unless melee does knockout its not an effective combat choice, penetrate, and knockback allow a minigunner a perfect shot or few shots.
In most games if you let some schmuck sneak up on you and wham you in the back with a knife you deserve an insta death not a oh hi BAM.
Since I don't PVP I can't say about knockback that much. But if it leaves even enough AP for a shot its not doing the job right.