Poles definitely do not fit in with Western European powers, because the Polish-Lithuanian Commonwealth was too backward compared to Western Europe. The Romantics call Poland the bastion of Christianity and the frontier of Western civilization, but the fact is that Poland was not part of Western civilization. The early modern Poland is closer to the Russians in terms of civilization than any Western civilizations, even though it is a Catholic country.
Poles civ, if they were to appear in AoE 3, would be either alone or in tandem with Ruthenians civ (or another name for this civ - Ukrainians or Cossacks) and potentialy with also Tatars civ. With the addition of the Poles civ, there should be an update of the Russians civ and the creation of an Eastern European Architectural Set.
Polish civs paired with Danes and Prussians civs just don’t fit! Poles, Ruthenians and Russian civs would perfectly fit together in an Eastern European Architectural Set. You can also give these civs some common things.
I once created a topic about the concept of creating an Eastern European DLC: