That comment is reckless exaggeration.

However, the purges of the 30s had a VERY significant impact on the Soviet Union - at least, at the time. Many military historians firmly believe that the extent of the purges in the officer corps of the Red Army were a direct contributing factor in its disintegration in the face of Operation Barbarossa in 1941. Not only was the military poorly-led and in no condition to fight the Wehrmacht, but Stalin's policies of collectivization and the elimination of the intelligentsia had alienated the citizens of the western reaches of the USSR. In many places, particularly in Ukraine, villagers welcomed the Germans as liberators, which took away one of the big advantages of being a defending army retreating through one's own territory. Soviet historians estimate the casualties sustained in that operation at over 4 million total in just 6 months, a number which likely would have been lower had there been more conciliatory policies in place in the years leading up to the war. For a quick and easily readable overview of the Soviet Union at war, I'd recommend Richard Overy's book "Russia's War".

It's a bit of a misnomer to label the purges as an attempt at "consolidation" for Stalin's rule. After Trotsky's murder, there were no real challengers for power in the Soviet Union. Yet, Stalin's paranoia at securing Soviet power, and his uncanny ability to see hidden domestic threats everywhere he looked, were a primary catalyst for the purges of the 30s. The intelligentsia is always a prime target for this sort of thing - the vast majority of revolutions and social upheavals have come from educated classes, rather than proletarians. Even the Russian revolutionaries of 1905 and 1917 were led by intellectuals rather than actual proletarians, and every good dictator knows that any realistic threat to his power will come from those educated enough to recognize injustice and think for themselves.

As for demographics, there is certainly still a noticeable effect of such a massive loss of male life in those few decades. Many of my female Russian friends lament that all the good ones died and took their genes with them, but there's really no scientific evidence that would support this - even before the revolution, Russian society and culture was fairly similar to what emerged afterward. Also, it would be difficult to claim that only the best Russian men were killed off in those years, as there was plenty of death to go around, and practically everyone was dragooned into the Red Army at one point or another. The Russians are not stupid, contrary to what that commenter seems to believe. Most of what seems irrational and extreme to us is a perspective grounded in a history which is basically a thousand years of autocracy and consistent exogenous threats.