To be honest, it's _easier_ to do nice functional-programming in Javascript with ES6 in my opinion, just due to the cleaner syntax for destructuring assignment, lambdas, and block-scoped variables.
Pretty much the only thing JavaScript had going for it was it's simplicity. Maybe simple is the wrong word, perhaps smallness is better. Sure js packed a ton of wtf into a small language, but once you grokked the weirdness of scoping etc. you were set to understand almost all its code. This is even better if you restricted yourself to the "good parts" ala Douglas Crockford as pretty much all js devs do now. It is a crummy version scheme that you actually get to use in your day job.
Sure arrow functions and "real" classes are objectively better, but I'm afraid of how enterprisey devs are going to react to them. I can foresee Java style coding guidelines being imposed upon es6 that would be very much opposed to functional styles of coding. It is a bit immature, but a lot of the hesitancy for es6 seems to be of this sort of fear that the Java dev culture will feel more at home with es6 and then stop ignoring js possible changing js dev culture in the process.
CSS? Put that sh!t in feature freeze, like, yesterday. Because javascript.
Javascript? Put that sh!t in feature freeze, like yesterday, because wasm.
Except... at least the reflection API's seem to "get it"—that you can't just keep adding features willy-nilly. I'll take a new metaprogramming feature that deprecates an equal number of old ones. And if you look at the MDN article the OP referred to, the reflection API is apparently intended to obsolete several existing built-ins. And as the OP also indicates, Proxy also lets programmers implement things that would otherwise be the VM's job.
But of course, unlike the auto industry, we can't actually realize obsolescence, so, like I said, I agree with you.
I have to say, I do not like it either. The problem is that now the language becomes more and more impure introducing syntax and keywords left and right. The language lives inside browser. The old ways to do it will never go away, it will just get worse and worse and become a mixture of all kinds of patterns. All of this just because some people cannot wrap their head around scoping and prototypes.
I am fine with the rapid pace of change in tooling or libraries, but I think browsers could improve in other areas (DOM), so we could still move forward.