There were 3 main issues with Feral Flare that Devourer doesn't have.
- The number of camps required to transform Wriggle's Lantern into Feral Flare meant that many champions had to powerfarm early to get the transformation at a reasonable time, meaning they wouldn't be ganking lanes.
- The on-hit healing scaled with your stacks, so some champions could powerfarm a Feral Flare to 40 stacks and have 50 healing on-hit
- The damage tripled against monster camps and minions, so Feral Flare junglers could clear Dragon and Baron very quickly
Devourer has fixed most of these issues: it doesn't need to transform, it doesn't have any healing, it doesn't deal extra damage to monster camps, and it gives 2 stacks for champion kills and assists which incentives junglers to gank and teamfight more than Feral Flare did. These changes, combined with the increase difficulty of the jungle, camp spawn times, and experience changes to jungle monsters, have greatly improved the item.