Yeah... JS and the DOM are incredibly fast, but that does not applications written for that platform are fast. Many JS developers have absolutely no idea how these technologies work and are reliant upon several layers of abstractions that are each progressively slower than the next.
As an analogy crypto coin in theory is a good idea, but its rife with fraud because most people playing with crypto are speculators that have no idea what they are doing.
You're totally right about the layers of abstraction... still, JS and DOM could be incredibly fast (and in some way, they are, sa there are huge optimizations behind for that to work as well), but they remain slower and more energy hungry than (almost) any native interface, even if you leave away all the layers of abstractions.