'Disorder' will always be a nebulous concept because it's an abstraction that encapsulates a dissatisfaction with the fitness of a person's psychological complexion in the context of the person's environment. Hyperactivity and a short attention span might be a disorder for a student who must focus deeply on a single concept, but an advantage for a hunter-gatherer who must integrate a large number of shallow ideas simultaneously. Thus I will humbly refrain from taking a strong stance on your questions; I can imagine situations in which each would be advantageous and in others the opposite.