I love Garen. But he is a monster in ARAM.
Don't get me wrong, I love he is a strong pick right now. I like him. I like that he has a nicer late game in Summoner's Rift.
But in ARAM he just means Victory. And that's it. There is nothing you can do if the enemy team has Garen and there is basically all you can do wrong and still win if you have him on your team.
Every game I've played him or seen him in a game I've been playing, he has always ended up 20+ kills and 1/2 of deaths (20/7, 24/10 etc).
I know any tank can build
and
and have a nice health regen to not have to die to recover. But Garen has it sooner, faster, he gets tankier, and deals 3 times the damage.
It is just insane.
As much as I love him I'd understand if they would just disable him in ARAM until he is fixed because now it is completely toxic and not fun.
is a monster on ARAM too, but... for the most part, games are balanced around Summoner's Rift.