I agree that jungle diversity has been a problem for RIOT.
One thing is that
is not played in any professional games that I've seen (Worlds or LCS) meaning it is a solo queue only item.
So you might think the problem is the strength of Devourer and that if you just tweak it it will become viable. But that isn't the problem.
Similarly you might look at top jungle picks in professional play and think that you should nerf the ones being played and buff the ones not being played. But this also misses the problem.
The reason certain junglers (
) are being picked right now at in pro play is that they have qualities preferred in the META. Strong Early Game and Ganking power is foremost among those. The ability to conveniently incorporate a
is also important, particularly if you can do so before finishing your jungle item. Also in pro play the jungler is usually not a carry. Koo Tigers' Hojin went carry Lee Sin, but this is more an anomaly of getting 4 kills at around 5 minutes and suddenly being in the carry position and embracing it. Pro teams don't try to funnel kills onto the jungler in the early game. What I mean is that there are qualities players are looking for when they play jungle professionally.
Another important factor in the problem of jungle diversity is the volatility of the jungle. Small changes in the jungle can have a large impact on the champions preferred. This creates a FotM effect where buffs or nerfs to champions don't promote jungle diversity but just make a different clique of champions in "S tier".
I think RIOT has to be cautious about the changes they make in the name of jungle diversity. There is a lot of potential for other jungle picks to become top picks with just slight changes in the META, but it's just as easy to knock them out of META.