How to begin, there is this thing among people who say they read economics or who usually usually identify with being libertarians, liberals, neoliberals and so forth that LTV has been disproven and such and such with Subjective Theory of Value etc. but they make this claim as though it were a hard science but there are discussions to whether economics is even a hard science at all and is actually a "soft science", if the latter is true then one could say that STV is no more wrong or right than LTV, at the end of the day all economics is just social relations related to production and consumption and wealth distribution which history will show is organic and ever changing. If we talk efficiency, human ingenuity has always had a great tendency towards efficiency no matter what system it adopted.
If we accept the fact that all past socio-economic functions of the past and present are constructs born out of the unique conditions each one rose out of then we can dispense with the idea of "hard science" or "soft science", and get to what matters which is class and exploitation. Socialism or Communism and it's main goal is addressing exploitation and class conflict and creating a system that eliminates it. All history is indeed class conflict, with the beginning of civilization and the ideas of "right to property", where once we largely shared the land commonly, when we began to settle we began to have our private plots, in order to protect that property we needed a system outside all the tribes that was to enforce these laws of "property" and so it begins.
Right to slaves, right to serfs and the land they worked, right to charge rent on land you own, right to the means of production and extract surplus value from labor. You can use my tools and I'll pay you a wage, a wage you have no control to choose. A serf partly owned the means of production, paid taxes to his Lord in the form of his crops and tithes to clergy, where a wage worker doesn't own any of the means of production.
The LTV doesn't mean that in a Socialist system workers will be paid the full value of their work but rather it's meant to expose the system of exploitation under Capitalism, the extraction of surplus value for profit. Under Socialist system there would be deductions made of course, some to go to the state and common funds of society, some reinvested back into the firm and lastly towards the workers themselves, is it "State Capitalism" if some of a firm's surplus value go towards the state? No because that surplus is redistributed back into society in the form of healthcare, education, job creation etc. No one person is exploited.
Of course even in Socialist society corruption would exist and specific politicians would find ways to full their pockets or strengthen the bureaucracy but it's our job as Communists to take steps to removing the power of the commodity form of money, it won't be abolished outright but with the right policies and determination it can be done.
I want to comment on China a little bit, there's questions to whether China is State Capitalist or not and I'll give my own opinion, they're a mixed economy with a mixture of Socialist firms and Capitalist ones in their "special economic zones". It's obvious that there's more exploitation there than in Socialist firms, is all this revisionist and stagist, yes but it's not our place in the west to say they're wholly the enemy of Socialism, to do so is to lack any form of critical thought. Should we criticize China? Of course… Marxist are supposed to be extremely self critical as well as critical of other Socialist states when they're doing wrong, but to completely write them off is nonsense drowned in pure ideology sniff we learn and we criticize, we criticize and we learn.