The great danger in a knife attack is that the assailant will not charge you but will get close to you as in arms reach and begin the attack. The method is highly unlikely to be slashing and most likely to be stabbing multiple times with short jabs.

In that case the attacked has to be able to block the jabs while either retrieving a gun or disarming the attacker. The problem with drawing is that it takes one arm out of the fight reducing the ability to block with either arm.

I can say this, it is easier to take a gun away than a knife. However a decision has to be instantly made about drawing or disarming or holding off until you can clear a draw. All bad decisions.a

I explained how I was taught to respond to a knife attack while in the Corps in posts 39 and 50 in this thread.