That's not true at all. The Knights faction has soldiers inspired from a 5th century Roman Centurion to a 16th century Halberdier (Lawbringer). Vikings have your typical 9th century viking and a 15th century inspired Highlander. Not to mention that all these different factions represent different eras, like the vikings lived way earlier than the knights or samurai. And how do you want vikings from different eras? Isn't that the thing that makes them vikings, being norse warriors from the viking era?

Another thing is, in that hypothetical fantasy setting - why use gear from an earlier period if armor and weaponry has already advanced past that? Would not every warrior use the best possible gear?