Tbh, they need to remove that from Renekton, and consider making it into an item. Like, there's very rarely any time that shield breaker is going to be relevant, except into very specific matchups. As in, Kench, Janna, Sion or Kled. Sometimes Kai'Sa. And into those very specific matchups, there should be a very specific way to go about it.
In TFT, Sword Breaker builds out of two defensive items...so it's an item that if they were to put into actual LoL, would probably give average or mediocre Armor/MR, and a passive to allow you to disarm. Since Disarm is honestly a horribly unfun mechanic on the rift, Why not make a Shield Breaker item with an active that allows your basic attacks to break shields for 5s on use, and lets say a 75s cooldown on end of effect? People complain that tanky champions do too much damage anyway...why not make a defensive item that gives them a short burst of shield-smashing power, in exchange for picking up an item with mediocre defensive stats and no actual damage increases? inb4 "lel assassins", I doubt ADCs/Assassins would want to pick up a tank/bruiser item with bad defensive stats and no AD, even if the active lets them ignore some defense, and since it's a niche item, it's something that'd only really see play in those very shield heavy matchups.