No,it's not fine, it's a horrible language,with a few good features that saves it from being a catastrophy.hence "Good Parts".
Or we wouldnt be here talking about Flow,Typescript or others if the language was "fine". JS was clearly not designed for what we are making out of it today.
But since there is no way around Javascript in webdev,good or bad,it doesnt even matter.It exists.TC39 isnt going to fix types,so types are fixed in userland.hence "Flow".