Wait so Sword Saint comes from Chinese, but Paizo implemented an archetype called Sword Saint under the Samurai class, which is Japanese? And then put the Kensai (which logically should be the version of the Sword Saint that is a Samurai) under the non-Japanese Magus class? This is making my head hurt.
Either way, yeah, there is no Samurai class in Kingmaker and there are no Asian names, so the name "Kensai" would be out of place. I wish they had ignored the archetype altogether and implemented Staff Magus instead, personally.
I believe the first to be implemented was the Kensai class a la BG2, and that one was based on the Chinese wuxia type swordsman: fast, melee specialists who don't wear armour and depend on speed and agility to dodge attacks. They called it using a Japanese name.
Then 3.5 came along, and in Complete Warrior (I think, please check), they introduced the Kensai class, which has no Oriental counterpart (what with enchanting your own weapon, etc.).
However, the melee classes were underpowered, so they introduced the Tome of Battle: The Book of Nine Swords, which "updated" the Fighter, Paladin and Monk via Warblade, Crusader and (you guessed it) Sword Saint respectively. This was explicitly stated to be based on the wuxia movies, and their strikes, counters and stances were very wuxia. Well, wuxia is Chinese, not Japanese, specifically made popular by a slew of Hong Kong movies and serials dating back to the 80s (think Bruce Lee era).
Paizo then took up everything 3.5 and did their own run on it, but with
very little understanding of the history or the meaning of the names. They basically just copied the names and added in kewl stuff that seem to be in line with the name. Typical Paizo copy and paste kitchen sink crap, in other words.
So, yes, making your head hurt is the ultimate result because Paizo, with typical Paizo-ness, have no fucking idea what they were doing.