How unrealistic are duels between samurai depicted?

Naah, the Japanese didn’t build pyramids.

In addition to Seven Samurai and Yojimbo, one should also mention The Outrage, which re-imagines Kurasawa’s Rashomon (!) as a Western. (!!!)
I’d love to see this film someday. I’ve read part of the script, and seen some stills (they’re in Grove Press’ wonderful edition of Rashomon, which includes not only the script, but also both stories the film is based on and a slew of great essays on it and Japanese cinema), but never seen the film itself. The cast is outrageous:

Paul Newman (as a Mexican ! – The Toshiro Mifune character)
Clair Bloom
Howard da Silva (Ben Franklin!)
William Shatner as a Preacher
Edward G. Robinson (as a con man)
Laurence Harvey

The earliest instance of the one-stroke duel I have seen, by the way, is in The Seven Samurai. When they redid it for The Magnificent Seven it became a throwing knife vs. gun duel, with James Coburn. Coburn, with his long face, looks astonishingly like Seiji Miyaguchi (as “Kyuzo”), the Samurai he’s essentially playing.