I... huh? Yeah, of course real swords need the user to be agile and stuff, but why bring it up in this context? There is no "finesse" weapon tag, there is no dex stat for damage scaling. Agility affects accuracy, while strength affects attack power for any physical weapon.
The only katanas I can think of in this game would be the balanced blade and the swift sword, the first of which is a light one-hander while the other is a two-hander. If you're thinking of "light" as meaning "finesse" or "dex/agility scaling," it's not, it's the tag that lets you wield a weapon in the offhand for dual-wielding. If you're talking about stuff which enhances crits, those two katanas have special effects that enhance crits, but the crit bonus stat itself only increases your chance to land one, actual crit damage most of the time is scaling from your cunning stat.
I don't think there's even a longsword in this game, unless you count the Spiraled Blade, Captain's Greatsword, and Galon's Griefmaker because of their being two-handed swords (to be fair, the Galon's is labelled as a bastard sword, so either it's seen as "also a greatsword," or it's a hand and a half, essentially a longsword). It would be neat to have one normal, actual longsword, but I'm not sure where the stuff about finesse and dex in regards to this come from.
Also, small thing, but I'm fairly certain it's spelled gambeson.