Good point. I do not consider China and Russia's attempted autocratic imposition of "communism" internally to be imperial expansion or colonialism.
As for the sheer numbers, centuries older colonial empires only killed fewer because they lacked the means, e.g. fossil fuels and machinery.
You may want to include Russia's autocratic imposition of communism on their satellite countries and their use of Russian troops and KGB operatives to suppress any dissent. Take a look at Hungary in 1956 or Czechoslovakia in 1968 as examples.
This is on top of a long history of Russia back to centuries of using brutal suppression to subject people. Take a look at Russian imperialism since 1500 -- it is well documented.
https://en.wikipedia.org/wiki/Russian_imperialism#Russian_colonial_expansion