Regarding your last paragraph, the Extensible Web Manifesto was created to encourage new APIs to expose low-level capabilities that can be extended and smoothed

Regarding your last paragraph, the Extensible Web Manifesto was created to encourage new APIs to expose low-level capabilities that can be extended and smoothed-over by libraries, reducing the surface area of privileged browser code and giving web developers more control. Whether or not the Extensible Web Manifesto is successful or not remains to be seen.