ES2015 rolled up around five/six years worth of changes since ES5 (which we could call ES2009, I suppose), so of course it's going to feel like it standardized a bunch more stuff.
The new system is faster as annual releases, even if it seems like ES2016, and ES2017, seem "light" relative to previous standards.
Sure there is a bunch of proposals, but after ES2015 only a few per year are included.