qutebrowser is not technically a "Python web browser". The GUI uses Python Qt bindings, and the browser engine itself is QtWebEngine. Python is simply the glue that ties it all together, and any language could be used instead, since performance is not a concern. This is why there are so many small niche "web browsers", such as Luakit, Nyxt, surf, etc.

Surely performance is even less of a concern for a set of tools applying one time patches to ungoogled chromium?