Every juggernaut in League has pretty much one counter: Staying the fuck away from them.
If Garen closes to you, you die.
Darius closes to you? You die.
Mundo closes? You die.
Illaoi closes? You die.
Morde closes? You die.
Nasus, Olaf, or Renekton close to you? You die.
Yorick closes to you? You die, and you lose a turret or two. Maybe three.
Urgot closes and lands a Q? You die.
I understand you main juggernauts, so you don't really see that happen, but, trust me, that's how it goes for every other class (except tanks after laning phase (since that's their job), or 2/3 of the divers and skirmishers (Since they're pretty much busted)). But for mages, ADC, supports, assassins, and the skirmishers/divers that aren't busted right now, that's just how it is. Their only way to survive is to stay the fuck away.
Now, if juggernauts were to lose some of the damage, the defense might be able to be buffed, or they might be allowed to be a bit more resistant to kiting. But their ability to close can't be buffed until it's possible to survive them if they close.