>>8780136Uh, this is true of all bladed weapons, even spears. Contrary to the myths you've chosen to believe, it's insanely difficult to pierce plate armor with any success, let alone slash. Chain mail is easier, but still offers good protection.
And, again, contrary to the myths many people choose to believe, 99.9% of soldiers and mercenaries fighting in the European Middle Ages or the Japanese Feudal Era wore light leather armor at best, sometimes studded leather. People weren't decking themselves out in heavy armor a whole lot, for one it was insanely expensive, two it made you extremely slow and clunky, three it made you fucking hot as hell, four you had to be in amazing physical shape to support it (which most people weren't). Armies were not about to invest in good metal armors for grunts and people who bought their own had to buy whatever they could afford.
Knights and shit commonly wore plate for ceremonial purposes and while commanding on the battlefield (the biggest reason for doing so is actually to protect against arrows). It was common in jousting tournaments. In real battle? Not so much.