"Are "non White" machinists really that much of a problem?"
All they need to be able to do is assist AI-led machinism, which they are more than capable of doing. (And eventually AI will no longer even need them as it takes over the entire operation.)
"I know there are some machinists in China, but aren't they just doing it to compete with the "Whites"?"
This is true in the sense that they would not be doing it if "whites" had never existed, but untrue in the sense of what the machinists themselves think about what they are doing. When they are doing machinism, they are not thinking: "If only we didn't have to compete with "whites", we could quit today." They are thinking: "WE ARE PROGRESSING HUMANITY!!! WE ARE SO COOL!!!" In other words, they have fully bought into the worldview of progressivism. So even if all "whites" magically vanished tomorrow, they would surely continue doing machinism. It would probably take at least until the last graduates of Western compulsory schooling have died off before we get a new generation that does not take progressivism for granted. (But if we are unlucky, by then AI will be able to do it all on its own already, and so it will still be too late.)