Polack jokes didn’t just fall outta the sky. There was good reason for them. Basically Poles are a less efficient German. That isn’t a complement.
My long term understanding is that Polack jokes were created by the Nazis as propaganda to undermine stiff Polish resistance. The story about Polish cavalry charging tanks is also a bit of Nazi propaganda and is absolutely not true in the way it is intended to be believed.
Yes, Polish Cavalry did attack German tanks, but they knew what a tank was and they used anti-tank rifles. The horses gave them better mobility than soldiers running on the ground. They would ambush Nazi tanks and then run.
Goebbels came up with the propaganda to make Polacks the butt of jokes.
I don't know any Poles personally, but from what i've seen of their history, they have been a force to be reckoned with. I think they may be as good or better than Germans, but they were clearly outnumbered in WWII.
Poland has the highest IQ average of any European county.
A cynic would say this is due to immigration to and from Europe.