"Here is a partial list of large scale communist states that failed dramatically. Russia(and most of Eastern Europe), Vietnam, Cuba, Venezuela, North Korea etc..."
Russia and Eastern European states didn't collapse but merely fell victim to revisionism. The earliest being the USSR with Khrushchev, but the actual decline happening around Brezhnev. Rest of Eastern Europe were forced to adopt Revisionist policies after the USSR went revisionist and abandoned Marxism-Leninism.
Vietnam is an interesting case in that the USA literally bombed the living shit out of Vietnam, economically blockaded them and had agent orange sprayed everywhere and damaged their nature and people. Imagine if that was all done in the USA, the USA would struggle to recover forever, only a few havens would exist if they were untouched by bombings. Also regardless, Vietnam fell to revisionism after Ho Chi Min died.
Cuba barely did any revisionism at all with Raul Castro, only implementing such because of US economic blockades that was harming the country and would destroy a Capitalist country if they were put under the same stress. Regardless, Cuba is veering away from Revisionism under Miguel Díaz-Canel, a Marxist-Leninist that won't obey under pressure. In fact, that's why the media went quiet after he became president - because the USA can't extort their successes by showing how Cuba is crumbling to US demands.
As @anarchyhasnogods already shown, I don't want to repeat for them. So let's go to the DPRK, or the Democratic People's Republic of Korea. They still waive Juche, an application of Marxism-Leninism that already agrees with the majority, if not all of, Marxism-Leninism and isn't revisionist to both ML and Marxism. But you are probably talking about Songun, they dropped it a long time ago as they finally reached nuclear capabilities and don't need to expand their military. It shows with how the economy has fared well recently - but of course you'll say something Orientalist like the people are brainwashed and are robots. In that case, I like to see you prove that by actually talking to them - they possess every emotion and have unwavering feelings towards the Worker's Party of Korea. Because, idk, maybe because charismatic leaders in general make people feel good about the party they represent and also the fact that the party didn't betray them or their interests as human beings. If you want to talk about cults of personality, then denounce every monument towards an American hero ever, from the founding fathers to John F. Kennedy to Ike (Eisenhower) to even Reagan. Because certainly people would die to even shake their hands and have a photo with them, because maybe they were just that charismatic and benefited people's interests for their time period. Sort of like how the Kim family has been benefiting the people's interests and see them as a steadfast, charismatic group of people. Regardless to even that fact, the DPRK has been setting for ages to slowly abolish the powers that president has in the DPRK and make it more and more to the people, because maybe they don't have to worry about being constantly invaded and can breathe for one second. Though economic blockades will persist as the USA doesn't want a Socialist state to even succeed, which makes you think how Capitalism doesn't want competition across ideologies.
"China is communist in name only. They have a controlled market, but they have embraced free trade and capitalism and they are now prospering."
Though I will get unto this point very soon, your point of the death toll has been answered by @anarchyhasnogods. I suggest you watch the video she linked.
Now unto this point, China (PRC, People's Republic of China) had been under a market economy when Deng took ever and was hellbent with his revisionism. Albeit Mao did went senile at a very old age, Deng would do far worse and kill off any anti-revisionist in the country that wouldn't be in line with Deng. In fact, the Tienanmen Square was a protest full of Maoists, MLs and Students that didn't agree to Deng's rule and policies in the PRC. He would allow Capital to flow into the country, destroy the communes and allow foreign Capital to dictate the whims of the people, that'll eventually help generate a Capitalist class in the PRC.
Years later that trend would be reversed under Xi Jingping's leadership, setting into motion with his fourteen points firmly established: trends like the killing off billionaires if they had gotten to rich, excluding them from the Party function, imprisoning corrupt party officials if they mismanaged funds for their ends, help combating poverty created thanks to Deng and Co.'s policies and expanding democracy back towards the proletarian path and ridding China of foreign Capital. Xi Jingping also is a staunch ML and is continuing to return China back on the revolutionary path with the proletarian masses. The PRC may still have remnants of Capital inside its country, but it has mercilessly, for the past few years, been forcing it to be under proletarian control and eliminating foreign control over the PRC.