In order to buy the (high-value) products China makes, the global south will first have to make money. And to make money they have to create and then sell high-value products themselves. Being an intermediary or a mere assembler is not enough.West will survive for decades behind that tariff wall but Chinese products, especially capital equipment and infrastructure, will make the rest of the world, the Global South, wealthy and advance which in turn will create more business for China.
China went through that phase and graduated to making its own stuff, often cheaper and better than the West. That hasn't happened so far for the rest of the "global south" and I doubt it will happen in the future.
Agree with your points that a Chinese supply-chain could be an opportunity for some of them, but would Chinese businessmen really prefer Nigeria over South-East Asia?