Speaking of how much Chinese and Japanese have in common though, here's an interesting NeighborNet typological chart of Northeast Asia:
Besides the tripartite Sinitic / Micro-Altaic / Japonic–Korean division, note also features like
modern Japanese and also Ryukyuan drifting closer to Ainu;
Jurchen-Manchu drifting closer to Sinitic and then back again (??);
the relative difficulty of separating "Altaic" from "non-Altaic" languages of NE Asia
Atayal hanging out close to Old Chinese and indeed within the authors' division line for Sinitic (many other SEA languages might fall around here);
Russian hanging out in the upper right between North Tungusic and Yukaghir (in a larger network most of Indo-European and also Uralic would probably attach somewhere around here).
(from Yurayong & Szeto 2020: (De-)Altaicisation as convergence and divergence between Japonic and Koreanic languages)