https://www.hoover.org/research/stalins-genocides
https://en.wikipedia.org/wiki/List_of_massacres_in_the_Soviet_Union

That's nowhere near complete.

Also, it didn't stop once the SU ended.

All in all I really don't think we need a race for higher numbers here, once a certain number has been reached. And it has been reached by both USA and USSR/Russia.