Devourer is NOT broken
What's broken is the synergy of some champions kits and on hit items.
Every champion who builds this jungling item always end up building
and maybe
. The synergy between the champions and these items are too strong.
Also most champions who use this item have some sort of on hit effect in their kit already

Tldr:Devourer isn't op in text, but when combined with these items/champions it makes the item look op.
(Maybe the most op thing about this item is that it's meant to be a late game item but is usually finished around the 20 minute mark. Maybe bringing down the amount of stacks skuttle and dragon give could help stop this or increase the amount of stacks before sated. Other than that, this item really isn't that op.)
This is more Cost Efficient then
When bought before any stacking is done.
Let alone 