That’s the show which convinced my brother a Samurai would defeat a Viking in single combat, then he tried to use it as evidence to prove it.
He was a fourth degree black belt and in college at the time. So, no excuse.
Deadliest Warrior is entertainment in the same vein as the nature shows that stack animals against each other in CGI battle to see who would win. It has no relationship to reality or any real value as it fails to take into account important details like context, experience fighting on foreign soil, and, you know, metallurgy. It is just there to entertain you.
The katana they used in that episode was one of the modern, high quality steel blades, possibly one of the ones tempered with liquid nitrogen that supposedly cut through car engines. Real katanas made from Japanese steel are vanishingly rare, worth somewhere around a million dollars or more, degrade very quickly, and are forged from low quality iron, which is the main reason why the katana is folded so many times during the forging process.
The Vikings had better armor, armor and weapons made from a higher quality of metal, shields, and more experience raiding on foreign soil against an unknown enemy.
Who would you put money on?
Deadliest Warrior doesn’t take much into account when plotting out their fights, and they don’t really do a good job delving into history for its category. While some history programs are exceptional in their discussion, the Deadliest Warrior isn’t history. Hell, Human Weapon’s premise was dumb but still it was generic but more accurate. Programs like this are there to sensationalize and entertain, not educate.