You’re right that Mao has to be understood from the perspective of historical imperial rule but I think you’re conflating a lot of different murder into one big “justified” blob.

No. I'm not. Even the concept of justification itself is suspect. The process occurred the way it did because of the historical and material context in which it occurred. That includes mistakes, excesses, and abuses. The net result was positive and there were no other alternatives except in the minds of idealists who are examining the process at a remove. This is what the term critical support means. The CPC itself acknowledges the mistakes, excesses, and abuses of Mao as such. There is no need for anyone to say those things were justified, but there is also no need to say that the reason the movement for communism is bad is because there are mistakes, excesses, and abuses.

We can recognize the legitimacy of resisting imperialism, landlordism, and the Kuomintang’s repression while questioning the concentration of political authority in the Chinese Communist Party and the violence that came out of it.

Questioning is healthy. We should question, and we do question. Liberals answer with "and therefore it never should have happened and it should be undone". Communists answer with "It was bad. Shit happens. We'll do better next time if the context allows." What do anarchists answer with? Usually with "communism is horrible and should be abandoned as a movement and resisted with anarchic violence."

This feels like the populist “anarchists just don’t like following rules” take.

Oh absolutely not. No one likes following rules. The problem with anarchism has nothing to do with their preferences for following rules. It has to do with their position that ideas are more important than material reality. For example:

There are plenty of mechanisms in a non-totalitarian society for rejecting drug abuse or foreign manipulation

No. There aren't. There are ideas about these mechanisms, but there are no successful implementations of these idea. Communists were the same way for a while. When communism was a theory on paper, it was totally unprepared to deal with reality. But no one actually believed that there were "plenty of mechanisms" for organizing a communist society. In fact, the reason the communist left the realm of theory and actually became a world historical process is because the theory explicitly acknowledged that it did not have the answers and it needed to actually go through the messy and difficult process of actually seizing power and then governing in order to advance its theory. Anarchism is much the same way. It has never actually succeeded outside of small enclaves, much like the communists had the Paris Commune, but it is completely indefensible in the face of actual existing power structures.

To repeat, this is the problem with anarchist thought. You believe that there exist real solutions to real problems that could be employed and yet there is no actual existing proof of such mechanisms and certainly none that have worked at the scale a nation even 25% the size of china. Anarchists are willing to tear down and disrupt actual existing anti-imperialist movements in favor of on-paper ideas about how it's entirely possible to dismantle imperialism without mistakes, excesses, and abuses. Anarchism is idealist - ideas have primacy over reality.

Anarchists would typically do

There is no such thing as "anarchists would typically do". There is no typical anarchism because no anarchist society lasts very long and there is no consistency between and among them because the ones that do exist for any amount of time operate at a microscale so that they never actually get the opportunity to face the majority of large-scale power conflict problems. What you mean is that "anarchists would typically theorize" because there are exactly zero anarchists communities that have resisted one of the top 5 European imperialist empires specifically on the axis of drug trafficking backed up by a power asymmetry like what China faced with England at that time, or anything even remotely comparable.

given the nature of drug use/abuse that methodology also provides a more effective counter given what we know about human psychology

For it to be effective, it would need to have an effect, which means it would need to be implemented. Theories are only shown to be more effective when they are put into practice. You are confusing your more parsimonious theory with a theory that has been put into practice and had a real world effect. The Chinese program to eradicate opium addiction took 4 years. The addiction at its peak was 10% of the population, 27% of the male population. That is fucking massive and the Chinese approach resolved it in 4 years.

If anarchists want to claim to have a more effective counter, then they're going to need to implement their program and show an actual effect at scale and over time while under active imperialist siege.