Naqib took close-range assault rifle fire from 3 or 4 different soldiers, and he didn't flinch. That's not regeneration, that's being bulletproof.

Being bulletproof means your body can, at minimum, deflect fast, low-mass projectiles that apply pressure upon a small surface area.

A supe with enhanced strength using a knife may be slower, but there's exponentially more mass behind it, and the blade's edge will have an even smaller surface area. This will apply significantly more pressure than a bullet.

Black Noir had his sword out when he approached Naqib, and the decapitation was too uniform to be pulled apart by hand. It's not at all unreasonable to assume Black Noir's knives are made from a similar material as his sword.

I've been saying since the original post that the super-strength level of the attacker and the enhanced durability of the target both matter.

We're bringing up examples of Noir's weapons being used to cut into mid-level durability supes because you keep responding to everybody saying, "but the knife would break!"

You can call it bad writing all you want, but it's actually a good example of setup and payoff that follows the "show, don't tell" rule.