Not trying to sell CoffeeScript here but most reasons of the author for dropping it looks more like a fault of the developer instead of the tool.
* Ambiguous syntax? Just add a few parenthesis.
* You don't like the existencial operator? Learn some JS, being able to easily differentiate between a truthy value and the existence of a variable with a single character is as sweet as it can get.
* Comparing a language to Babel? Doesn't make sense. Babel translate ES6/2015 to ES5 for compatibility. Comparing ES6/2015 to CoffeeScript makes sense.
* CoffeeScript is the reason you couldn't scale/solve data syncing or redrawable views? JS/CS/TypeScript/etc have nothing to do with that! Maybe he was thinking about Backbone?
Seems like the guy is confusing tools and languages... and making (bad) decisions because of that.
Personally I'm not going back to writing { }, return and ;'s :-)