Knights were considered stuff of legend because they were ultra violent warriors, raised for war since birth, with massive armors and charging on horseback.
This is simply badass.
Counter argument is that the samurais have a similar status in contemporary pop culture and we cannot say the saved Christianity.
The figure of the warrior will always be appealing
It varies from country to country I think.
In Spain you are more likely to have the Conquistadores or the soldiers of the Tercios as the symbol(s) of the great warrior.
Italy I think is the condottieri but I might be wrong.
Portugal is the Templars, the Explorers and the Captains of the Age of Discovery that are the symbols of our great warriors. The last were by far the craziest and more brutal of the group.
Basically every culture has his version of the Greatest Warriors and I think that the Miles Cristianus only got that famous because of the English fixation with Knights.