I was delighted for Joe when he was appointed but also very fearful Bully, knowing that an away Ashes tour was looming. I think Cook's resignation was also skewed by knowing this.
Going to Oz without ammunition and then without a world class fighter of an all rounder was always going to be trouble and, as you say, making Joe captain because he's the best player, is not a valid reason.
Before England he's captained Yorkshire TWICE, once at Lords when he set over 400 and they got them and then at Trent Bridge when Gale was banned and we were champions elect.
Previous tactical captains,eg Brearley, Illingworth were wily hardened pro's or great motivators ( or both) and trying to get the best out of an increasingly petulant Broad, an out of form, disinterested Cook , a bits and pieces spinner/batsman, a few rookies ( a couple of which did well) , an ageing leader of the attack and a few medium pacers picked off easily was always going to be difficult.
Joe will fight through it and will have learnt so much but will have to take a lot of stick in the coming months.Just as long as it does not erode his magnificent batsmanship he will come good.

