Tachi and katana are not modern nomenclature, they are precisely what the Japanese called the swords and the styles for using the swords. They have a different balance, weight, and center of gravity. They were used differently and for different purposes. When we are discussing rules for a katana, we are talking about a katana, not a tachi nor a uchigatana.
Im inclined to believe he is totally right on this
http://www.homejapan.com/japanese-words-1
From what I've gathered, what we know as a katana, and what they know as a katana, is a different thing. When we hear "katana", we think of a sword with a particular set of common attributes/physical qualities. For them? Not so much. I can find more if you like, but that link also has its own external references that support its assertion which can easily be viewed/referenced/verified.
Obviously 'cut through anything' is an exaggeration. When you use a katana one-handed, the balance is off, which means you set yourself up for weak cuts that need to be over compensated. That also means you leave yourself open for an attack or to even have your sword knocked out of your hand by a skilled opponent. Not that there isn't some type of exception to the rule out there. Hell, a person can go around using a zweihander one-handed. That doesn't mean the sword wasn't meant to be used two-handed and is off balance if used one-handed.
The "balance is off"? May I ask in your opinion what kind of balance
is ideal for one handed use? Though I must admit I cant help but find this notion just a little funny, as I can readily cite you numerous historical
one handed swords, which have a point of balance as far or even
further away from the guard than what was typical for a "katana". Good swords. Scimitars, kilijs, shamshirs, talwars (just to name a few), etc. Many of these weapons typically have points of balance anywhere from 6, up to 10 inches out away from the hand guard on average (With historical katanas averaging around 6, give or take an inch or 2). Which begs the question, were these one handed swords (Most of which are well known to be very good weapons) ill fit to be one handed swords (Maybe you know something the users and smiths of these weapons did not?)? I can also cite hema practitioners/teachers who contradict what your stating here (Ie this fellow has quite a few interesting things to say in regards to balance specifically:
https://www.youtube.com/watch?v=YPnxBIMZ31I), So I must ask, what exactly are you basing this assertion on? Can you cite anything? Id love to see. And the concept of a "weak" blow is also a bit befuddling to me. Can I ask you to elaborate? Again, I can provide references demonstrating that the difference is quite questionable (ie this chap here:
https://www.youtube.com/watch?v=bqrvqKhIcL0 most of his channel is devoted to swords and how they were used historically, many of his other videos are worth a look. he also generally provides sources to support his claims and demonstrates where he obtained his information. hes also quick/glad to provide specifics if he glossed over something and you ask him personally), so again I must ask what youre basing this on? Though I guess it depends on your definition of weak.
Dont get the wrong idea, I readily admit/agree that a katana was
primarily intended for 2 handed use. But asserting its "off balanced" for one handed use, or thatd itd be weak when used so, and etc? Apologies on my skepticism, but Id *love* to see what drew you to make these conclusions. Can you cite some sources to support your claims? I can not stress enough, Id genuinely love to be proven wrong. I care little about being right, and more about knowing the truth. Maybe the sources Ive provided are false, I hope you dont mind but Id love to see yours,
Thank you
As for the topic at hand; Personally, like others have stated, I'd just give it longsword stats. I feel giving it any clear advantage in such a way with 0 cost to the player kind of diminishes the value of the other weapons, for no real reason that I can see- Other than because someone might feel that it "should" be better (regardless of whether or not the logic used to support such a feeling is or isnt sounded in reality). I find the names in the weapon index to be arbitrary, using them merely as place holders of weapons "like" that, and quite often use the weapons stats, but describe them as something else entirely. It seems players Ive encountered like imagining/having the visual in their head more than they care about the stats.