WW being good has nothing to do with Devourer (which is actually weaker than Flare - no triple damage to non-champions, no sustain, 600 gold more expensive for -5 initial damage counting for Flare's AD and 20% AS more (600 gold, exactly), weakish build path).
WW being good has more to do with Skirmisher's Sabre and the fact that sustain means something in this jungle.
I'm sorry but you are just wrong in your comparison between Devourer and Feral Flare.
You can stack Devourer much earlier in the game, so vastly higher snowball potential. Feral Flare takes 30 camps to stack and has 25 onhit damage. This item has 40 onhit damage at start (so equal to Flare with 15 stacks) and is available significantly earlier (300g cheaper overall then FF, don't know where your math came from) - you can get it by the time you've reached level 6, so you can have it well before 10th minute of the game.
However, Skirmisher's Sabre is also part of the problem as well -- and combined with being upgraded into a Devourer and adding true damage on top of everything makes it 10x worse. Warwick can strait up 100-0 anyone that isn't building full tank items right now during his ult alone. Ridiculous.