Ok hol up. Your perception is extremely skewed. It's not that garen out damages adcs, its that their damage is more noticeable against champs that are very squishy. You see their health bar going down slower because they have MORE hp and MORE resistances. they don't necessarily do absurd damage, they can just survive long enough to kill you, if they can even reach you. Garen is designed to be a juggernaut, not a straight tank, he has no hard cc and they only way he'll kill you is if you go to fight him. He is immobile and his only engage to run at you, and he's weak to people who can kite him.
You play fighter champs, and you build damage. You are dumping damage into your kit without considering how that damage will affect fights. If you're using that damage to target the garen, you're doing something wrong. Wukong and Kayn can EASILY go around the frontline to kill the carries, so do that. You have to understand how juggernauts work; they WANT you to go in and fight them head on, that's where they excel. Look at darius, garen, yorick, illaoi; they are all immobile champs that don't have the best engage. They rely on you getting into range of them and their abilities so that they can punish you hard.
TL;DR: Tanks=/=Juggernauts. Don't fight a juggarnaut unless you can do so while staying out of their range. Don't complain that a champ works the way they're designed to.
P.S. ARAM and Twisted are way different than summoners rift, and they balance champs around SR