In 1938 (or even prior), England were in no position to fight a ground war. And Chamberlain knew they didn't have the ability to conscript a large ground army and send overseas (they were just out of the Depression and post WW1). He also didn't have the US anywhere near willing to join - the opposite. When war was declared, there was a significant gap before fighting actually started in France and they were still wiped out pretty quickly.
But Chamberlain had no idea there would be that significant gap. He can get zero credit for that.
Yes, Britain increased its military resources between 1938 and 1940, but people are assuming in 1938 they would have confronted a 1940 level
Germany. But Germany was much weaker then too, it would have faced a two front conflict between France and Czechs, in that conflict Britain would not have needed the air defences of 1940.
In the gap the German strength was increased because of the munitions plants captured in Czechoslovakia in 1938 & the flow of materials from the USSR as part of the pact.
Britain's land army in 1940 was still small by Continental standards. Nobody expected Britain in 1938 to be fighting alone a ground war against Germany in Central Europe. So why was Chamberlain getting involved?
Stalin signed the pact with Hitler because he expected Britain and France to go to war versus Germany and so buy Stalin time to prepare for war with Germany.
If Britain and France had left Germany to its own devices re: Poland and Czech Republic, Stalin would have had to confront him earlier and certainly would not have signed a pact with him to supply resources and move his frontier forwards to a less defensible position. Britain and France could have waited for Germany and USSR to wear themselves out then intervened.
Or, they should have confronted Germany in 1938 along with the French, Czechs and with Germany also worried about what the USSR would do.
I don't see the case for not going to war in 1938 over Czechoslovakia and instead going to war in 1939 over Poland.
I'm still sticking with Chamberlain as a dreadful prime minister. And Lord North of the American War too.