Out of the 6M Polish casualties 3M of them were Jewish, the Polish people suffered extensively during WW2 there's no doubt about it.
Both the Germans and the Russians often practices universal punishment and exterminated entire villages for hosting resistance fighters and later on for cooperating with either Russian or German forces.
The 6M death figure which is horrible is also the total death accounts during the war which included Pols that died while serving in the Polish army, Poles that were conscripted to the German army, Poles who were Conscripted to the Soviet Army, Civilians who died in massacres, starvation, and disease.
Poland isn't the only country in which the civilian population encountered such acts, Germany wiped entire villages in Greece for showing the slightest sign of resistance and then wiped the nearest 3 villages as a warning to others.
War crimes always happens, but not every war crime is a Genocide, Poland might actually be a unique case because of how it was split between Stalin and Hitler and because of the animosity the Germans had towards it for "stealing" large parts of the "fatherland" after WW1.
But again it's hard to equate the crimes committed in Poland to Genocide, especially considering that even during the War both the occupied Polish government and the exiled Government continued counting loses of "ethnic" poles, which at the end amounted to about 10% of the pre-war "ethnic" poles population.
But that could've as easily been changed if the war would've dragged longer and once the Germans finished dealing with their "Jewish Problem" they would no longer see the Slavic people as "necessary slave labor".
Wars are shit, WW2 and the Holocaust is probably the shittiest of them all, but if you ask the Poles would they rather be armed and fighting or be the next inline for complementary train tickets you would probably get only a single response and that is we rather fight, there are many ways to die and while we all like idolizing heroic deaths there is almost no one that would rather not fight and die than die in naked in a gas chamber.