Bad dice was pretty common during real WW II too
1941 Japan attack Singapore with 30 000 men, Brits defend with 120 000 men dug in + large fleet. In A&A this will equal Japan attack with 1 inf, brit defend with 4 inf and lose all.
In the German attack on France 1940, Germany attacked with 400 divisions and 2700 tanks, and France/Britain defend with 400 divisions and 4200 tanks. In A&A this will be like Germany attack with 20 inf and 3 tanks, and Allies defend with 20 inf and 4 tanks and lose all, while germany lose 1 inf. During Barbarossa it was even more skewed, and Russia lost like 10 times more men than Germany.
In Battle of Crete, Germany attack with 10 000 pratroopers and Brits defend with 50 000 men and have a large fleet in adjacent sea zone. This will be like Germany attack with 1 bomber and brits defend with 5 inf and loose all.
Of course in real wars you usually need to be 3 to 1 in attacks if you want to succeed, but as we see bad luck exist in real world too