All the living commanders are imbeciles.
The only one who was marginally competent was Jaime, for forming an infantry square. Yet even then it wasn't quite the proper formation. For one thing, you'd want forward ranks to plant their spears in the ground as best they could in the time they had. (Unlike a bayonet/musket square, where you quite obviously need the current front line to be aiming their muskets at the incoming charge).
As for the Drothraki, they only carried a single melee weapon. That's foolish. Your cavalry does carry a melee weapon, but also either needs a pole-range lance (to break the square) or a missile weapon, if they are instead mounted archers. Your calvary most certainly does not charge at an infantry pike square with pole weapons if all you've got is a scimitar and the momentum of a horse (nevermind that your horse might have a thing or two to say about crashing into ranks of pikes).
And Jon? Jon is just hopeless. I won't go on about the others...
Anyway, more general worries on the show's future:
https://www.theatlantic.com/entertainment/archive/2017/08/deus-ex-westeros/537480/