Scaramanga
Brickhead
I don't think the Hermit kingdom needs a naval unit that could challenge the Jong or aggressively bother Japan.I think it was less a statement of intent and more Firaxis trying to scrounge up famous admirals from different cultures and connect a retirement ability to them with the mechanics that were available in Vanilla. Just like replacing a City-State later on, Yi Sun-Sin's ability shouldn't preclude Turtle Ships.
What Korea needs is a Hero. And that hero is Yi sun Sin riding an ironclad.