Even without attributing the Chinese writing system to the immigrants from China, your post above does not contribute to the discussion. Japanese is genetically unrelated to Chinese and typologically different from it. What the Yayoi immigrants from the mainland originally brought with them bore no resemblance to the Chinese language. That the Japanese were able to use Chinese words and Chinese characters for their own purposes and some similarities between the two languages arose as the OP mentions, has absolutely nothing to do with pre-Proto-Japonic speakers coming from the mainland. All that meaningful Chinese–Japanese interaction happened many centuries later.