You're misunderstanding. There's no hand coalescing in Ember, and there's no duplicate work. If you change your models a thousand times in a row, you still get one redraw, fully automatically.
The same holds for dependent computed properties. If you change a dependencies many times in a row, the dependent property only reevaluates once.
It's still slower than ReactJS but much less so than before. In fact it's now #3 in that benchmark suite behind ReactJS and Backbone (and much faster than ReactJS in the completing benchmark), although I wouldn't be surprised if the other frameworks were set up as incorrectly too.
The same holds for dependent computed properties. If you change a dependencies many times in a row, the dependent property only reevaluates once.