There's no magic with Angular or Bootstrap, they're codifying an approach using 100% native JS or CSS. Even SASS and LESS are just alternative ways to produce CSS. This is not novel in computing.
You're not forced to use Rails for your server application, many other software exists as well as Rails: Django, PHP, etc. However you /are/ forced to use Javascript, CSS and the DOM; Unless you're a Big Browser Vendor and can try and coerce support (and even so, the amount of websites made in something like Dash is pitiful afaik). People made frameworks and libraries that make it bearable (SCSS, JQuery, etc), but that doesn't mean everything is solved...
Yet if I were to call coffeescript an overly complex javascript framework, people would probably strenuously disagree. But that is what it amounts to.
Purescript compiles down to javascript but helps save programmers from themselves by introducing a better type system as well as great data structures, and functional paradigms
Typescript adds static typing and OOP
CoffeeScript...is syntactic sugar? (okay maybe I agree with the coffeescript sentiment)
Although I don't entirely agree that compiling a statically typed language into javascript really helps much, since the end result is still... javascript in a browser.
But the last time I tried to defend that I got almost universally disagreed with, so I'll concede that the process might have value I just don't see.