It might. A good sword might cut into plate armor. But armor existed for a long time, and for a good reason. It worked. It gave the armored fighter an advantage over his opponent.
My blade has a Rockwell hardness rating over 60 (i.e., diamond or tungsten carbide level). It’s made of some seriously exotic stuff. Cost a small fortune!
For comparison, a typical axe blade has a hardness of 45 to 55.
I’ve cut up iron and steel pipes and bars with this thing. It’s also fairly flexible. Picked up a nick or two, but nothing serious.
Like I said, exotic materials.
Form factor is katana — what I trained with for about a decade. Folded a few dozen times, thousands of layer of differentially hardened material in it.
Now, armor made of similar materials would defeat it. Just don’t know many people who work with such (except my armorer).