Idea for making Garen more interesting.
How about making it so if he kills the Villain his R cdr resets and a new villain is chosen. This way he is encouraged to seek the Villain and kill them.
Hopefully this would make him more focused and rewarding to play. Because at the moment he just goes and kill the Villain and that's it. It feels off.
This way he would fit more thematically, he seeks justice. Justice never ends and so he seeks to eradicate the Villains.