It is true that the war was fought in the Soviet Union and neighbouring countries the figures for Leningrad alone dwarf all the allied numbers.
The high figures for the Soviet Empire was down to the incompetence of Stalin, who was an idiot. He decimated his Military Leadership just before the War, put only his weakest defences against their new joint border with Nazi Germany, refused to believ, when warned by a dozen different sources, that Hitler was about to attack the Soviet Empire, he admired and looked up to Hitler, worshiped him, based his own purges on Hitler's, and he froze like a rabbit when Hitler attack the him, and went into hiding. He was reckless with his population and numbers, it didn't matter how many of his people died, as long as he won. He was a brutal, ruthless leader, who murdered a lot more of his own people than Hitler did. He saw the War as an opportunity to expand his Empire, and was casually watching as Hitler and the Democracies fought it out, hoping to move in when the War had ended and beat the weakened victor. He wanted back the old borders of the old Imperial Empire, including Finland, Estonia, Latvia, and Lithuania, (most of which he got), he wanted to punish those Poles for defeating him in an earlier expedition to Poland, He had already got back Ukraine and Georgia and was making their life a misery deliberately creating famine to starve the population into submission, known as Holodomor. He bullied Finland into giving up territory, in Karelia. He had incorporated Mongolian into his Empire. He was one of the greatest imperialists of all time, one of the most brutal vile Dictators in History.
Estonia, Latvia, Lithuanian and the eastern part of Poland wer invaded and incorporated in the Soviet Empire as part of a deal with Hitler, his friend. Nothing to do with Churchill.
...It’s also true that the second front was deliberately delayed but the Soviets won inspite of this. The appeasement of Stalin was the only thing that Churchill could do to preserve what was left of the Empire that appeasement involved selling Poland out.
He was an Ally of Hitler until Hitler attacked him, he is the one that delayed a "Second Front". Britain was being bombed nightly and was already fighting in North Africa, Syria and Iraq.