In any case, it's quite likely Soviet Russia would have fallen to the Nazis in WW2. While Trotsky was arguably more benevolent than Stalin, it was precisely Stalin's psychotic ruthlessness that contributed to the Red Army turning the tide at the eastern Front. When the RA was defending Moscow, Stalin basically ordered anyone who refused to fight to be shot immediately. I doubt Trotsky would have done likewise. But then I guess that's neither here nor there.
Your reasoning is represented by the Stalin quote "In the Soviet Army, it takes more courage for a man to retreat than to advance". (Or something along those lines) There is no doubt a great reason for the ultimate success of the Soviet Union in WWII was Stalin's method of handling the military.
But the main reason I feel Stalin prepared the USSR for war and the main reason they were able to defeat the Nazis was his rapid industrialization of the Soviet Union. Under his watch the USSR went from an undeveloped agriculturally based society to a world manufacturing power. Of course, this started under Lenin (the Lenin quote goes something like "Socialism is Soviet power plus the electrification of the entire country". 'Socialism' isn't the first word of that quote, a word which eludes me, but it shows that technologically advancing the USSR was a goal of the CPSU from the very beginning.) Industrialization surely would have occured to a degree under Trotsky, but not anywhere close to what Stalin was able to create and I feel a Trotsky-led CCCP would have been little match for Nazi Germany, even despite the harsh conditions at Stalingrad and some help from the USA.
Of course assuming the USSR would have survived until 1940 under Trotsky, which I'm not so sure it would.