There is more that goes into an airplane than the people maintaining or assembling it, which can and does go afoul. There is the entire manufacturing process, how materials are sourced, processed, refined, machined/formed, heat treated, stress relieved, coated/plated, assembled, and the list goes on. That is a major factor why aircraft are so safe and if you think China's material and process controls are as rigorous as someone like Boeing or Airbus, it isn't. It has taken decades of actual aircraft manufacturing to get the formula right for those respective companies and they continue to evolve as time goes on and new information is learned.