And looking more broadly, how much of any given system's death toll should be counted, and in what way. Mao caused massive amounts of death with the Great Leap Forward, which arguably would not have happened under a system that relied less on central management and more on capitalism's distributed feedback mechanisms. Then there were purges, suppression campaigns, and land reforms that resulted in productivity losses.
But comparing that with a capitalist country that is a liberal democracy is hard. There are a lot of factors involved. Case in point: there was solid growth in China and the USSR. But we can't make a direct comparison between them and the West. China and the USSR were playing catch up using technologies produced by capitalist countries. Take tractors, which immensely boosted productivity. Those were sourced from the West, at least initially.