Most swords used were industrial made shin gunto's. Towards the end of the war, they started to lose quality. A tamehagane katana is not brittle, the spine of the sword was coated in clay and used different varieties of steel which all ended up with a sword with a softish spine which is less likely to shatter, and a hard edge which can be sharper than soft steel. Shin guntos are not tamehagane, they are a solid piece of non-folded metal. Also it did change over a thousand years, you could just look this up and find that. While someone not experienced in using a katana would probably have a hard time cutting instead of hacking, with enough force I think it would be pretty effective, especially with the overhead strike that i've seen in the beta. However, quite a few nco's had older better made swords, also those with these may have been somewhat more proficient than others. I think the sword probably (or does) has an advantage in speed, limb wounds and although it might not be as intuitive to stab with a katana, it would probably do more damage than a bayonet. Sorry for the rant