To address the betrayal by the West point he makes there is, in my opinion good reason for that. The first being what was dubbed "The Phoney War" or Sitzkrieg. Basically after the outbreak of war the expected course would be for the French and British to take direct military action. This did not happen, there were some minor attacks in the Saarland and some notable things happening in the air and sea but overwhelmingly the western allies did nothing until the Germans invaded the Low Countries 8 months later. Not only was this terrible for Poland it was arguably terrible for all the Allies. German Military Commander Alfred Jodl said something to the effect that Germany would have been destroyed had the western allies launched a serious offensive. There were 110 French and British Divisions to the Germans 23. How successful at mobilizing and invading against the Siegfried line these men would have been I do not know but many German officers said they would have only lasted weeks. It very well may have not ended the war but it would have taken a tremendous amount of pressure off of Poland and made good on the whole point of even having an alliance in the first place. The second, a much less valid complaint when one knows all the facts, is that towards the end of WW2 control over polands government as well as its future borders we're really more or less put into the hands of the USSR. Both Churchill and Roosevelt did raise objections and concerns at Yalta as well as propose a number of alternative solutions that the Polish people would be better served with but the hard truth was the Soviets were already well in control of most of the Former Polish territory at that point. The Secretary of State at the time, Edward Sttetinius, summed it up best "as a result of this military situation, it was not a question of what Great Britain and the United States would permit Russia to do in Poland, but what the two countries could persuade the Soviet Union to accept." In the end Poland operated as a Soviet satellite state and had very little independence until the fall of the Iron Curtain. In addition they lost a great deal of there territory in the east to The Soviet Union being compensated with german territory to the north and west. Thus a belief remains that the West sold out or stabbed Poland in the back. In reality the truth is much more nuanced, did they s everything in there power to ensure a free Poland? No. At the same time short of the threat of violence they had little power or bargaining chips to negotiate on the issue with and they certainly at least tried to get a more favorable deal. And to brush on your other topics Poland supplied around a quarter of a million troops after its fall to the war effort and they were active in pretty much every theater of the western front including North Africa and Italy. They provided a small but noteworthy number of pilots (~5% of the RAF) who took part in the Battle of Britain and would continue serving in the air, sea and ground until the end of the war. And the contribution of Polish mathematicians work in deciphering the Enigma to the British was crucial in them cracking its code.

Poland made a significant contribution to the Allied cause.

Poland was defeated in 1939, and although Germany's modern and well-trained military, using also massive geographical advantages, would have inevitably defeated Poland it was the surprise intervention of the Red Army that really prevented the Polish Army from exacting a larger price from the Wehrmacht.

Polish airmen then fought for France and later Britain, Polish pilots being practiced and skilled relative to the average in the Armee d'le Air and Royal Air Force at this time. A Polish-manned Hurricane squadron (IIRC No 303) was the most successful of all in the 1940 fighting over England. Polish squadrons continued to be successful in the RAF right until the end of the war.

A Polish brigade fought in the siege of Tobruk and the Polish Armoured Division (of the British army) trained in Africa, later serving in France after D-Day where they were involved in an especially vicious battle to prevent Germans from escaping the Falaise Pocket after the Wehrmacht's defeat in Normandy. Polish troops also served in large numbers in Italy.

As well as stealing the Enigma machine and passing it to England, which underpinned the entire success of Enigma because the Germans did not suspect the British possessed a machine for some time (of course this was not in itself enough to read messages), Poles also provided much of the basic methodology for the Parachute Regiment- the British had not given any thought to paratroopers before the war and, for example, the Polish parachute harness was copied directly.

The Red Army built up a massive 'Polish' army to counterweight those fighting in the West, but this was almost entirely led by Russians given new 'Polish' identities. The Soviet commander Rokossovsky was of Polish origin, and prominent tin the fighting in the closing stages of the war including the liberation of Poland.