Indeed. The proper two-handed weapons, anachronistically called Zweihanders, became weapons used by larger masses of infantry in the renaissance era in Western Europe when they were deployed against the pike blocks (not cavalry). Which is why they are the only types of two-handed weapons depicted in Tsardoms.
Were there some sort of longswords possibly used as two-handed swords in Serbia? It seems so. But at the time the Serbian roster was designed over a decade ago it was decided not to include them as a separate unit. Could the Serbian roster benefit from such a unit? Sure, why not, at one point we could add it. But it will have to be a shared unit no matter what simply because now we are at the point of improving several factions at a time rather than only one faction.