When I said "the Soviet Union of the 20s and 30s", I thought it was clear that I mostly meant the latter part of the 20s (after the Poland-Soviet war) and the earlier part of the 30s (before Stalin purged the best military minds of the time). Regardless, the Poland-USSR war took place almost immediately after/during the Civil War, with the Red Army being in the midst of reorganization and many of the White forces either not integrated or still fighting against the Soviets. Anyhow, the Soviet military advantage peaked around 1934 or so, when it's new designs were state of the art and it's military structure was functional. After that, Stalin screwed things up in a variety of ways:
-His purges wiped out the bulk of his officer corps, with the result being that the Red Army of 1941 was horrifically understaffed, with those few officers still around being inexperienced and often incompetent
-He removed the territorial army of the Soviet Union and put it into the regular forces, depriving the USSR of extra competent manpower when it was needed most
-He appeased Hitler by providing him raw materials even when it was obvious Hitler was planning an attack. He also had anyone who pointed out the obvious imminent invasion arrested.
-When Hitler attacked, he required his officers throw their forces into bloody meatgrinders rather than fall back, resulting in massive losses for basically no gains.
-He was sufficiently tyrannical that the Nazis were able to recruit many Russians into anti-Soviet forces (an impressive feat considering how the Nazis treated those in the East)
Industrialization may have been slower without the Bolsheviks and, to some degree, Stalin, but its worth mentioning that Russia was already on that road as of the 1890s, and likely would have had a fairly strong industrial base by the 30s anyway, and probably with less unnecessary deaths too. Anyhow, even if you really like the Bolsheviks for whatever reason, Stalin was easily the worst of the bunch. He had pretty much every other Communist from his time executed for some reason or another.