Dear down-voter: The case of an arrow function asserting the type "function" and its prototype being `Function.prototype`, while not being subject to `call` or `apply` (for `this` being lexically bound to the parent object) is a practical case of introducing extra constraints – think of callbacks and the use of `apply` or `call` on them. (See the Harmony specs.)

So this is a) a personal view on this (as pointed out clearly) and b) not raised deliberately.