Well Poland do have a good quality spear unit in their Spearmen, especially with armour upgrades. Their Dismounted Polish Knights will beat Dismounted Portugese Knights in prolonged melee if they withstand the charge which they will. Plus Poland have one of the best cavalry units in the game in Polish Guard which outclass the Portugese knights, and Dismounted Portugese Knights would stand no chance against them. And of course Poland have Polish Nobles who are great javelin cavalry, and the manouverability of the Polish Guard combined with infantry can easily beat the Aventuros.