Vlandian's heavy cav has 204 cm lance, 33dmg, 54 armor, 25 horse armor, 260 horse hp (with correctly chosen perks)
Khuzait's heavy cav can have 208 cm lance, 29 dmg, 43 armor, 15 horse armor, 250 horse hp.
Empire's heavy cav is the only one that might take on vlandia with their longer "heavy kontos" and heavy armor, but good luck staying alive against all vlandian snipers.
Similar comparisons hold true for vlandian heavy infantry and ranged units. Basically vlandia has the full package.
Worst of it all is, vlandian peasant's price being 80 and the looter perk. This allows vlandians to spam every siege/tdm games with peasants, sergeants and knights. Basically peasants earn coins by spawning and dying, and if they get a kill they get +10 gold.