I would love to say that that was Yoshi's words on the matter of SAM being a DPS but that is not really the case, that reddit article is paraphrasing things, his actual words translated to more along the lines of:
"We considered using Samurai instead of Dark Knight, but thematically it didn't fit. Also, if it were a tank would it be more considered a Shogun? Samurai might be considered a DPS, blah blah blah please look forward to it."
It was more along the lines of conjecture than statement. I believe we can call it little more than a 'musing' of the idea whether or not SAM should be tank or DPS. Much like what we are doing now.
I'd love to ask you how you know how Dark Knight will play?
Now for a bit of schooling, as someone who is quite literally IRL trained to be able to train and use: Small sword, Rapier, Bastard Sword (Zweihander), and proficient in Aikido (a modern martial art technique derived from one of the historically older martial arts forms) I can tell you, while wield a Katana and a Zweihander you might have both your hands on the weapon, however...they are COMPLETELY different in functionality, In order to stop an attack with a bastard sword generally you would stop it head on perpendicular to cause the reverb to make your opponent lose their balance. With a Katana because of the creation of the blade you would allow your opponent to glide off your blade to deflect an attack which then would hopefully throw them off their balance. They function completely different, so please stop saying its the same thing as DRK, its not, nothing the same save for you hold it with two hands, in fact that is not entirely true because there are many times in Aikido training with a Katana that you hold with one hand and apply pressure to the butt of weapon or use your free hand to give the blade movements a more fluid animation for countering an attack.
As for Small sword and Rapier both weapons at a glance look exactly the same, most people won't even be able to tell the difference between the two unless you physically hold it. There is a big weight distribution difference which allows each weapon to do things better or worse than the other. I hate to call people out like this, but when you've poured hours upon hours to perfect a craft like I have its a bit insulting for someone to say "they are exactly the same" over and over. Again, I'm not trying to call anyone out, but before you claim its exactly the same go pick up those weapons in real life and tell me they are the same, the weight balance is different, the over all weight is different, the design of the weapon is different, which in turns FORCES the user to use it different; meaning it CANNOT play the same.