I guess you don't know much about biology, firearms or psychology then? First of all, the body has a specific reaction time in any given situation. The average is between 200 and 400 ms. That's a lot of time in close quarters. Then we have firearms. Firearms are most effective at a distance because they take longer time to aim at close range (try holding a book out, then suddenly jerking it towards someone - a loaded gun can weigh approximately that of a hardcover book). Then there's psychology. If someone hits you, your instinct is not immediately to shoot them, but to think of the pain. That's not something you can stop without years of experience.
If you haven't done it tons of times before (as in trained for it), a person with a handgun who doesn't intend to use it is not that hard to disarm.
If we're talking someone who intends to shoot you (like, imagine someone popping up at two metres to shoot you and only that), he will. There is no way to stop a person who intends to shoot you if he has the element of surprise. Then it's over.
The question however is whether the person being aimed at can maintain composure, and whether they have any training in hand to hand combat. If they maintain composure and have training, it's not that big of a deal to disarm a handgun.
Now, a knife... Good luck disarming someone with a knife.
I don't for a second believe you've talked to various types of people and they all agree with you on this subject. Most self-defence teachers (for instance some of your very own Israeli commandos) teach methods in how to easily disarm a person holding a handgun. I think you're just making it up to back up your claim.