That needs substantiation. It's not immediately obvious in any way.
About Babel, notice how we never had a problem playing with language-level features that target the PC? That's the difference a good VM makes (although on the PC case, it's not virtual). Besides, you are conflating VMs and languages somehow - they have only a tenuous relation.
> misses most of the expressiveness of Python and Ruby.
> It's more on line with Java
> viewed as a serious language is all because it has a
> monopoly on the browsers.
No, it isn't inertia -- one important reason is that creating a transpiler to JS invariably ends up with a crippled (feature-restricted), slower version of the original language (Clojure, etc.)
Thus the hope placed in Webassembly.
People generally choose languages due to assumptions about their hiring pool.
Engineers choose something like PureScript as it's not a 'blub' language and people think that by choosing it they will be able to hire (or be seen as) "math geniuses". I'm sure the feature set is important, but it's not enough to unseat a language with the previously described properties.
You can not inspect an object and change its type or the set of available properties based on some calculation.
You can not run some code in a controlled environment separated from your main code.