No one sane would take off their helmet in the middle of a battlefield for the most important fight/battle. You don't slice with a sword through plate armor or decent chain mail. It just doesn't happen in real battle conditions. For that matter, it's not so easy to slice through padded cloth gambeson armor! Also, the "reality-tv" shows that have covered historical weapons are often bogus. You "half-sword" to wrestle your opponent to the ground, then guide the stabby point of a specialized sword through an eye-hole or other gap in their armor. Likewise, real battles between knights didn't consist of them bashing at each other, using their swords crudely like glorified metal clubs.
Long exchanges of blows/parries in movies are just for show. In fact, there are fighting manuals that urge you not to parry if you can help it, but rather always "bind" a weapon in the process of some kind of counterattack.
Social class meant a hell of a lot. On the battlefield, it determined how much armor you could afford to keep up, which made a big difference to how likely you'd be killed.
Most swords were sidearms, not main battlefield weapons, analogous in role to an automatic pistol vs. an assault rifle. For most of western history, and in many other parts of the world, the main battlefield weapons were polearms, often used in conjunction with a shield. This even applies to a certain extent to Japan! (Though the naginata fell out of favor and for awhile actually became a sign of social status for women.)
Katana are not magic, and there were and are european, middle-eastern, and indian subcontinental swords capable of equivalent feats of cutting.