Pretty strange song.
They're singing this in order to honour the Polish soldiers who would perish unless they outnumbered the Germans 40 to 1 ?? That seems to sort of give a low opinion of the Polish to be honest.
Furthermore this fact sort of makes the metaphor of the Spartans fall away. The spartans were outnumbered, while the polish actually had more manpower.
The only thing "praise-worthy" for the polish soldiers was their sense of honour. They would rather all charge themselves to death instead of surrendering and running away. Especially seeing the charge of the polish cavalry divisions against the german tanks always sort of gives me goosebumps. Not just for the sillyness of it, but also since it signified a quick change in the way warfare was going to be conducted from then on. And in such a foolish charge there is an aspect of glory, stupid faith.
With regards to small nations hurting the german war effort one could better look at Malta and the Netherlands for example.
Malta who sort of took out the remaining german para-trooper divisions + stalled them for a long while in their mediterranean expedition.
Netherlands, who eventually capitalated to save the cities from bombardment. As a matter of fact their army was not even defeated. They had had to regroup and form a new defensive line but that one was actually totally intact. Their only fault was that their 30 airplanes had all been destroyed during the previous war efforts. The 30 fokker airplanes, of which most were older versions, had taken down 100 airplanes of the Luftwaffe at the cost of their own lives. This left them with no secure means to defend against the bombers of the Germans.
So the dutch government surrendered in order to prevent bombings on their cities. Communication not being what it is now this led to problems. While Netherlands had already surrendered the hundred german bombers were already on their way to Rotterdam. Without being able to receive the retreat order they went on to bombard the centre of Rotterdam, killing thousands.