I suggest you do the following test: Buy a heavy dagger or a sword, buy yourself cut proved gloves out of Aramid, and buy yourself some leather gloves. Sharpen the sword real good. Put on the aramid gloves and then about this gloves also put the leather gloves on. And then conduct the hitting test, and think of ‘actio et reactio’. Every pull will move the sword and that will cut. There is a certain physics behind it (why a moving edge is sharper than a not moved) and it’s very complicated. This also a reason why a saber functions in a specific way, and why there are curved swords.
I know of a f…g idiot that has sharpened his Iaito to do some iaido. He has cut through this thumb tendon, only by doing a Noto.
I do not believe every shit that i see, especially on youtube. He is holding the sword a certain way to fool the people, but this cannot be done in a real fight. And also i know that in a real fight everything goes not as planned. For that video i would kick this guy in the face, if i knew him, because he endangers the health of many people.
I like Albrecht Dürer very much, but i would not recommend what he depicts here, if the depiction would shown that he is holding the flat side against his hand then it would be ok. Wallerstein first one is a clear way to loss some fingers, the second one can be conducted but only with strong leather gloves.
So do one another test. Buy yourself a chicken leg, take a great and sharp kitchen knife and a hammer. Lay this chicken leg on a kitchen board, and then lay the sharp edge of the knife on the chicken leg, holding the knife on his handle in your hand. Take the hammer in the other hand and hit with the hammer on the dull edge of the knife. (begin with weak strikes) But do not forget to wear some protective glasses and garment on your body and your neck, before you conduct this ‘sophisticated experiment’, some knifes are cause of bad annaling process brittle and may fracture. And this may lead to very bad injuries, so be very very careful.
And believe me this hammer test is with much smaller forces, than the things that are happening in a real fight.