Everybody needs a knife. Everybody. Maybe not a shortsword, but a knife, of whatever shape, is an absolutely necessary tool. If these Yelmalions in question ever go into the field, every single one of them will have a knife, and some, perhaps many of them, will think "Hey, if I got a bit larger one of these, it would be handy for stabbing trollkin in close quarters, as well as for whittling kindling and cutting straps."
I suppose a Kopis might do, but I also recall that during the American Revolutionary times, it was commonplace for officers and soldiers to very, very quickly swap their regulation swords for tomahawks after their first time in the field. Easier to carry, less likely to snag in brush, more practical use.
As someone who has hauled a 9 foot spear through woods while wearing armor, I'll tell you it's a pain. TWO of them would be super annoying, even if one was shorter. And strapping a spear onto your back is an even bigger pain. Yes, of course there aren't woods in Prax and phalanxes never enter woods out of choice, but my points remain even when there's no brush.