I was wondering if this can also be applied to items?
Not really. Champions are exclusive to themselves and are affected by items/runes. Conversely, Runes/Items can apply to a variety of different champions so the comparison doesn't really work.
As an example: Let's say Yuumi has a 60% winrate. While it might be items she's abusing or a rune that's broken with her kit, the problem still primarily lies with Yuumi, which means we can buff her counters, nerf her kit or nerf aspects she uses.
Now let's say Athene's has a 57% winrate. However, Yuumi is pushing this up due to always building it. Conversely, other champs who build this item (Such as Janna or Soraka) only have around a 45-52% win rate. A bit of a spread but we don't know if this item is busted or not. Granted, there are times when items can be broken. Those cases are often because it raises an entire class of champions up. However, this could ALSO mean that the class of champion is meta, such as when IE has a massive winrate because so many champs build it in an ADC meta.
So some criteria for if an item is BUSTED busted:
- A low usage item has a massive winrate (AKA: Only Volibear builds Bear Gloves. Bear gloves have an 80% win rate)
- A high usage item with a high winrate across some classes (All supports building Banner of Command)
- A high usage item with a decent winrate across ALL classes (Everyone using Thunderlord's Decree)
TL;DR Items have far more variables for why it could be/is broken than a champions do.