The millions of their own killed are coincidental to the act of their great power.
Stalin was a monster, but he made them great, so goes their thinking
This is why they could never understand the Poles - both are Slavs but their mentality is so utterly different even at an individual level: you get 2 Poles together and you will have 3 political parties. poles love to debate, argue, disagree. But Ruskies don't - they get hot and bothered and will stick to the "party line"
Stalinism was a natural fit - Stalin was the Red Tsar.
Even under the Tsars, the Russian peasants were treated horribly - worse than Poles or other conquered peoples were, yet the Russians didn't revolt against the Tsar
It's what Stalin said "Communism in Poland is like putting a saddle on a bull"
True that Russians dont see Stalin as a Communist. They dont lump him in with Lenin, Brezhnev, etc. He is beyond ideology, they see him as a modern-day Ivan the Terrible, who also just happened to be Stalins role model. To him, the Bolsheviks were just a means to gain power.