Devourer is never going to be a balanced item

It's always going to be shit tier or totally break the shit out of a few champions

Even further to that point, it's never going to be good in competitive play because junglers don't get the luxury of much income since vision is so important and transferring what little gold and exp they get to other laners so they can carry. It's why junglers who are strong in competitive rarely change, it's about remaining relevant on limited income and this is why you see Gragas, Rek'Sai and a few others because their jobs are straight forward, have decent base stats and bring utility to the game that they don't need items or gold to have.

This means it's just a solo queue stomping items. On some champions, like Aatrox as an example, it dramatically increases their power but in exchange it breaks the shit out of other champions like Kayle, Shyv and even Yi. Some of these champions need direct changes because their kits are a cluster fuck of random power (Kayle), some of these champions naturally have absurd synergy with itemization like this due to the nature of their kits (Yi/Shyv) while still having other options that make them good (Shyv can build cinderhulk, Yi cna build warrior). The point is, some of these champions just need direct changes to fix their busted ass kits so itemization like this doesn't push them in one direction so heavily.

The issue you run into is that devourer is actually fairly balanced in principle. It requires farming or massive snowballing because the components don't give you a ton until you complete it, then you're required to get 30 stacks. But it's those few champions who complete this and break the item and as a result, you either gut the item (which is a short term fix) or you gut the champions who are abusive with it - which is also a short term fix but creates problems as you destroy champions who are already a cluster fuck of bad design but on top of that, the item likely gets nerfed too so you hurt them even more. In reality, Kayle needs direct kit changes and needs them badly. Shyv probably just needs nerfs if the item is going to remain in its normal state but these nerfs need to focus on her jungle power, not her lane power. Yi is already pretty pub stompish as it is, he's extremely binary regardless. He either stomps or get stomps, very rarely is there any in between.

But the item itself probably has a few things wrong with it that can be addressed, but it's just going to make it shit tier again. And this is a small patch to champions who were otherwise in pretty miserable states as it breaks them, so what's easier? Nerfing those champions or the item because both present problems. In reality, the item just shouldn't exist and you address some of these champions individually and you can reintroduce a new AS item that gives scaling based on AS or something, like buying AS increases its on-hit power and there isn't a farm element attached to it.

So tl;dr, scrap this item concept. You tried it with Feral Flare last season and it broke the game, got gutted and the same thing is happening again with a similar approach. Address the individual abusers accordingly, for better or worse, and reintroduce the item to not be so farm based and binary in gameplay (because let's face it, someone either snowballs out of control and farms it up quickly or they don't, spend half the game stacking it and have lost because their lanes got pressured and put behind). I guess this would mean next offseason will be spent on the jungle, AGAIN, and fighter rework gets pushed back another 3 years. It's okay, we are the Duke Nukem Forever of promised reworks.