Sorry, I can't help you with the quote. As to the sentiment, I disagree most strenuously.
The knife is dynamic, like the empty hand. What the person who said this is neglecting is that with a knife in your hand, certain empty hand movements are superceded or made redundant. For example, how do you check with a blade? You slash, hack or place. How do you block? Same thing. Since the blade is steel instead of flesh, we need not reconfigure it for different tasks as we do our hands. What the knife sacrifices in actual mutability it makes up for in speed, simplicity and destruction. Furthermore, the knife has possibilities not available with empty hand; trapping and passing in reverse grip is far more lively than the same without a knife.
Also, if you want to get fancy about it, grabbing and locking is also possible with a knife. You'll see some knife players in a modified saber grip, with their thumb hovering above the spine. This allows them to flow into joint locks, when the locks present themselves.
Finally, it's important to remember that when you have a knife in your hand, that's not your only tool. What about your check hand? The check hand, properly integrated into knife play, is capable of all those things the knife hand was capable of before you put a knife in it.