While he makes some valid points. devs are using these languages because a lot of them just dont like javascript, and will never like it.
You cant design a language and expect every developper to agree on these choices, especially when it's the core language of a plateform (web).
So choice is good,nothing is perfect and javascript is far from perfect itself.
Coffeescript is productive and influenced ES6 heavily, Dart has its own ecosystem,Typescript fits people who want compile time type checking. And what language devs choose is nobody's business but theirs.
Front end devs are not interested in writing javascript,they are interested in using web apis and building products. At the end of the day,the user doesnt care about the language,but wether he can run the app in his browser or not.
It's funny the OP use Crockford citations, Coffeescript was an answer to Crockford's book at first place,and D. Crockford loves Coffeescript.