I'd prefer to see mechanical nerfs to strong champions.
Most of the game's power creep and balance issues comes from increasingly complex kits which are really no harder to play than simplistic counterparts, because so many of the mechanics are often handled naturally in the champion's abilities or just occur beyond the scope of player input. Things like yasuo's double crit and armor pen, malzahar's reworked W, ekko's W passive execution, or a plethora of other secondary effects or passives attached to abilities which also have actives.
For example, on the PBE, Mundo was given this on his E
Passive: When Dr. Mundo suffers magic damage, his magic resist is increased by 2% for 2 seconds, up to a maximum of 6/12/18/24/30%
which changes nothing about the complexity of the champion or the player input, but does act to increase the champion's power and range of situations which the champion handles for the player inherently.
These kind of handicap mechanics are the kinds of things i'd like to see nerfed out of champion kits. Make players learn to make their champion strong against different types of enemies, not just hand out free power and countering.
Now i understand that a good number of these effects are added to make the champions feel unique, but if they want their champions to feel unique, then they should treat these secondary effects of an ability as the primary aspects and give players a degree of mechanical accountability for making them powerful.