I don't think stealth archers are overpowered. I've played a bunch of different play styles on Legendary difficulty. There is definite useless skills in my opinion. Alchemy and poisons became weak and underwhelming on higher difficulties without abusing craft skill boost. You can kill pretty much anything with a dagger assassin build with Nocturne shadow ability, dark brotherhood gloves, and duel weilding master blacksmith deadric daggers.
The most efficient build for fighting dragons in my opinion is a sword and board build with restoration and Spellbreaker to block the dragon breath.
The only thing needed is to remove for balance is shouts. 3rd tier mark for death was far more powerful than any piece of equipment or skill build. Takes the most powerful thing on Legendary difficulty and makes it easy to kill.
