I’ve often been critical of individual decisions by Churchill (notably failures in Greece and then Malaya where he repeated the mistake of committing scarce ground and naval forces without adequate, and in comparison with the enemy no, air cover), but when one considers the many competing demands he had on his resources he turned out brilliantly as the leader of the only nation fighting the vastly superior Italian and German forces for a year and a half after France surrendered and before America and the USSR came in, without which there could and would not have been an Allied victory.
I am inclined to think that Churchill’s greatest fault was rampant aggression which produced a desire to try all sorts of hopeless operations against Germany from Norway to Greece, but it was also his, and Britain’s, greatest strength as the Germans and Italians thought they had cornered Britain at various times in various places but Churchill’s aggressive spirit kept the fight going. I doubt any other British, or later Allied, leader would have done the same, and certainly not the British lot he replaced at a critical early time in the war.
At a strategic level, Churchill’s greatest fault was a belligerent desire to fight his enemies and a consequent willingness to ignore the basic military principle of concentrating forces at the enemy’s weakest point in preference for fighting the enemy wherever the opportunity arose, which was spectacularly illustrated by his decision for political purposes to take critical forces out of North Africa to a doomed campaign in Greece, which lost Greece and British forces as a minor repeat of the previous loss in France. It could also have lost North Africa, which then would have pretty much lost the strategically important parts of the Mediterranean and potentially the Iraq oilfields and various other not critical to Britain’s war but, if captured, useful to Germany’s ability to fight the war.
However, compare the early years of the war with Hitler and Mussolini who were both in the ascendant, and Stalin who was carving up Europe to his own advantage in collaboration with Hitler.
Churchill’s aggressive, tenacious character puts Mussolini’s posturing emptiness in the shade; overwhelms Hitler’s hubris in time and, as a Prime Minister who routinely carried a Bren gun in his car in case of German invasion, demonstrates a character who would fight to his own death rather than, like Hitler, commit suicide to escape capture; and condemns Stalin’s self-preservation.
As for Tojo & Co, certainly aggressive and tenacious, and stunningly brutal and inhumane, but not very bright in the long term tactical or strategical aspects which essentially were: Let’s grab this and see if we can hold it after attacking the only major power which can crush us after, to our considerable surprise despite warnings from better informed elements within our own camp, we’ve outraged it beyond belief by a sneak attack on Pearl Harbor.
Roosevelt is in his own category, as the calm and determined leader of the only nation which has the industrial, never mind the military, power to change the balance against all Axis powers.