It is different on the street. Different surface. It could be dark. And there are no rules.
It is like comparing apples and oranges.
In terms of conditions, you do what you have to do but in essence what you are saying is "if you don't see the knife..." Well yeah, if you don't see the knife because it's too dark you won't know to use the proper techniques but if you can see the knife you can use it. The surface doesn't really matter for the arm grab, if you can do your move you go get control of the arm and the Gracie video I showed illustrates a technique to use if you can't zone to the outside say due to being in a narrow hall way.
Are their times/circumstances where you can't do it? Sure, this however applies to every single MA technique. To say "under circumstance Z it won't work" doesn't mean that under circumstances A-Y it isn't the better choice.
If you tried to grab a persons arm mid shank you would get gutted as well.
I mean it is almost impossible without a knife. But we just flail around hoping to get lucky.
By the way you never mentioned if you fought one knife guy more times than a hundred knife guys.
In terms of mid shank yes, you are going to take a hit, but if they are doing the classic prison "sewing machine" shank you are still better off getting control of that arm. If you don't, while you move through to do an inside guard take down that sewing machine is still going to be shanking the hell out of you.
Yes unarmed against a knife wielder is dangerous as hell but if you just charge in there you are basically saying "kill me".
As for actual knife fighting I do full on sparring/competition al la the last video I posted, though we use chalked blades at the moment we haven't gotten shock knives. If you don't go for that limb you end up "dead" every time, the other way you often end up injured but the times you end up dead are far less.
A few things here. First only need to look at two arts you named to try and defend your position, Judo (also thinking Jujutsu) and HEMA, when you add FMA it becomes more clear. When you look at the traditional Martial Arts documented to be used on the battlefield, that we have records of the techniques they evolved techniques, even when from completely different cultures, specifically designed to deal with a knife and they do it by controlling the blade wielding limb. When different cultures over centuries develop the same thing it is rather telling and if those techniques weren't necessary they wouldn't have evolved so universally. I actually found it odd you mentioned Judo and HEMA for this reason. If someone is arguing you don't need to address the limb wielding the blade but then keep naming battlefield martial arts that evolved techniques to control the limb, it just seemed odd. Even the HEMA video you linked showed this (controlling the blade with a blade to execute the take down) and the article had a woodcut of an unarmed person controlling the limb of an armed person.
When you next add to that the fact Modern Military and Security Forces train it this way you have additional proof because these groups don't train things that they haven't validated.
