While possible, I see this more of an example of a combination of ignorance and arrogance than definitive proof that Garleans can't utilized enchanted items. Few in the Empire even believe that savages would be capable of creating such items - and for those in the know, why would they bother with these trinkets when Garlean technology can provide all the benefits and more? It wouldn't be the first time in history that a belligerent nation has turned away a technological advantage due to prejudice and racism.
Zenos, on the other hand, is a bit more pragmatic when it comes to magical items (at least, when they are katana), and has no pride issues about using their magic in combat.
While Zenos wields katana because he thinks they're neat, it's also stated that he's a COLLECTOR of rare and interesting katana. While he carries several at once, each katana does have special properties that he makes use of in combat. While he no doubt like to have several at hand so that he's never without a weapon when his katana breaks, I don't doubt that he also likes to stock a variety of katana with different effects for different situations.
And yes, everything is better with spinning!