I don't think Riot understands this concept so I'll explain it in the context of the latest Devourer nerf (increase in time to acquire Sated and decrease in the final damage provided).
Let's say that Yi and Shyvana are a balance issue since they have the best synergy with Sated and the most success in ranked. Given the state of competitive play, this may not really be objectively true but suppose it is. Shyvana and Yi are now pretty much exclusively junglers so we're not considering the effect on other roles. You can nerf the champions or you can nerf the items.
If you nerf the champions, the scope of disruption is minimal and limited to two champions. Alternatively, you can nerf the core item, Devourer or other possibly problematic items. Some suggest that Rageblade should be nerfed to address these junglers and in principle this makes sense. Ideally, you want to nerf more specific items deeper in the tree rather than very general ones since that typically creates less disruption. However, Rageblade isn't actually core on either Yi or Shyvana. If you look at Masters+ players on the Korean ladder, you'll find many Yis and Shyvanas opting for BoRK or TH without ever buying Rageblade. Thus, if Riot wants to nerf an item to address them, it probably would have to be Devourer.
Unfortunately by nerfing Devourer, you create far more disruption than just nerfing the champions because that affects ALL junglers who may opt. for that route. This includes possibly abuse cases like Shyvana and Yi but also dozens of others like Kench, Nocturne, WW, Vi, Volibear, Ekko, Aatrox, Kindred, Kayle who aren't even an issue right now. In fact, for many of these, such as Volibear, Vi or Ekko, Devourer isn't the best choice anyway. However, nerfing the item reduces the cases where it's situationally strong or at least viable and lowers the diversity of Devourer junglers in general. For example, Devourer Vi may not be ideal but it is excellent vs tanks and so it may be a decent choice vs tanky teams with weak early games. Nocturne (especially in high ELO), tends to go Warrior but if your lanes are early game oriented and won't need help, you may prefer to pack a bit of a stronger punch late game. After the proposed Devourer nerfs, taking Devourer situational becomes a thing of the past. It simply won't be worth it except on the best users of the item. In effect, all it does is polarize the viability of Devourer junglers even more towards Yi and Shyvana while leaving currently mediocre Devourer junglers like Nocturne or Aatrox completely in the dust. It creates a lot of disruption for many junglers and in effect reduces both build diversity as well as jungle diversity to avoid touching the kits of two junglers.
This doesn't seem like the right way to handle things at all even if Riot actually believes there's a problem with some Devourer junglers. The approach is akin to putting Pneumonia medicine in the water supply of an entire city instead of just providing it to those with the disease. If you don't like that analogy, consider if someone poisoned the water supply of an entire city to kill rats in the sewage system.