Way too many C#/Java developers who used JS in the early 2000s and hated it still think it's the same language.
I'm wiling to bet C# is 10x better than the last time I used it. Except, I don't have a good excuse to use it again to see.
I think I can probably say that Javascript engines are an order of magnitude faster than they were 16 (!) years ago.
If I may make a generalisation, C#/Java devs are more likely to be "enterprise" developers and said enterprises were more likely to be the ones on IE <11. I know I fought damn hard to upgrade from IE8 just a couple of years ago. My webdev skills suffered as a consequence, too.
Microsoft moved pretty fast once they realised that IE needed to compete again - and Visual Studio evolved alongside it (mostly).
VS2015 is now a pretty good development environment for Javascript/Typescript and even includes some Grunt build support (although I haven't had a play with it yet).
Two orders of magnitude. I just checked, and on my laptop http://web.mit.edu/bzbarsky/www/mandelbrot-clean.html (the first JS thing I wrote where performance of the language itself seriously mattered) runs in about 30-60ms in modern browsers. On the same hardware, it runs in about 2200ms in Firefox 3, which is the last pre-JIT version of Firefox. Other benchmarks I've tried show similar improvements results. And that's only going back to 2008; the interpreter was a good bit slower another 8 years before that.