Teams in competitive can pick early game teams and they know jungle pathing and warding to invade and a number of things that you can't expect out of solo queue kids. Devourer, like Katarina and other pubstompy picks or items, takes advantage of team disorganization and the inability to pick against and play around it. But it's impossible to foster that kind of environment in a team without being on voice chat or having prior experience. It creates a really hairy situation for the item because it has no place in a 5's or competitive environment and is only used as mid-late game insurance in solo queue. If you can't pick an early pressure jungler or a team that scales or can just stomp the early game, devourer just takes over the game.
Devourer and stacking jungle items don't really have a place in solo queue because they foster an attitude and playstyle that doesn't belong in the jungle spot at all. Junglers are assassins or bruisers or tanks or AP fighters, they're not hypercarries. They simply don't have the gold to do so and if they did they'd be the most overpowered role in the game because they also have the element of surprise and roam and gank potential and the ability to make plays that other spots don't have because they have to, y'know, CS.
So the problem with devourer is that you're now giving a champion the ability to hypercarry without a lot of gold, all it takes is time and farm. The way to exploit this is with teamwork, but that's not a viable answer in low elo. It needs to be removed from the game because it adds an unhealthy playstyle and champion pool to the jungle. Kayle and shyvana aren't junglers, they can be PLAYED in the jungle, but Kayle should be getting gold, she should be used as a niche counterpick to assassins. Shyvana was a staple top laner for a good portion of season 4. She's used because of her tank stats and scaling. What needs to be put in the jungle are people that make plays, people with CC, and utility.
Now this ofc brings up the argument of "Oh well you're trying to pigeonhole the jungle into being a utility bot. Why can't we have hypercarries in the jungle?"
I just told you why. It's too safe to farm in your jungle and hope that your lanes don't get screwed. The risk is NOT congruent to the payout because the risk comes from solo queue players being able to work together and use pressure to exploit the times in the game where these champions are bad. Additionally, you can even do all that and they can still come back guns blazing at 30 minutes with their completed sated devourer and blade of the ruined king and split your team to death. Who can 1v1 these people?
Jungle isn't a position that should be getting pentakills, they're the position that gets first blood. It's flat out easier to balance around that and frankly it's healthier for the game if the other 3 enchantments are the ones that existed in their current state and devourer didn't exist.
But what about some of these champions now? What do we do with attack speed junglers like Nocturne or Master Yi?
Well there's much healthier answers than giving them ways to double their blade of the ruined king current health. There's better ways than pigeonholing them into farming their jungle or only getting crabs because they give 2 stacks. What if there was a flat attack speed item with magic dmg, sustain, and a ward on it to promote their defensive, farmy playstyle? I'm not giving my answer to the new attack speed item, but Devourer, in its current state, will either be trash or WAY WAY too good.