Well you could also build your web startup in a compile-to-JS language and barely ever touch JS, and you’d also be fine, right? (Maybe in rare cases for interop

Well you could also build your web startup in a compile-to-JS language and barely ever touch JS, and you’d also be fine, right? (Maybe in rare cases for interop, debug, etc) At any rate you’re right - the dominance of each language for their respective use cases (JS-Web / Py-ML) emanates from different sources.