Let's Talk About Smite
I think the biggest corporate to jungler power being so high are the champion smites on a spell that should have all been about PvE (player vs environment) and securing objectives. By giving them both that and the ability to ignite+exhaust (red smite) or nuke+slow (blue smite) is giving them essentially 3 summoner spells at all times, this is going to have some power creeping issues.
Smite upgrades I do think are a good idea, but I would rather see new ones where they are either about amplifying the PvE game in some way, smite more often or playing around the vision game in some way. Moving upgraded smites in this direction makes it where junglers are not getting excess power, moves them back more towards the supportive role that they were always meant to be, and allows for proper choice and options to choose the upgrade most suited for that game and your own play style.
I will give some example ideas to paint a little bit of a better picture:
Spectral Smite: Your Smite becomes Spectral Smite. Casting it summons a wraith that moves towards the closest enemy champion for the next 8 seconds, revealing the area around it and if it collides with an enemy champion then it applies True Sight against it for 4 seconds and slows it down by 5% - 30% based on distance traveled.
Clairvoyant Smite: Your Smite becomes Clairvoyant Smite. Casting it reveals 2000 - 4500 (based on level) units around you for 2 seconds.
Crow Smite: Your Smite becomes Crow Smite. Casting it summons a crow by your side for 15 seconds, attacking one time and revealing the first ward that it sees for 8 seconds and then flies off. [Range: 1000 unites]
Explosive Smite: Your Smite becomes Explosive Smite. Casting it causes it to explode, dealing 25% of its damage to nearby non-champion targets and stunning all non-champion targets for 3 seconds.
(NOTE: Epic Monsters are immune to crowd control, so this stuns minions, non-epic monsters and other targets in the same classification. This is a help to junglers if you are looking for faster clears or need help with killing chickens and krugs.)
Restoring Smite: Your Smite becomes Restoring Smite. Allowing you to heal from any applicable target rather than only monsters. Additionally, this restores 30% of your missing mana or energy.
Quick Smite: Your Smite becomes Quick Smite. Your Smite's cooldown and recharge time is cut in half.
Executioner's Smite: Your Smite becomes Executioner's Smite. Your Smite deals 15% bonus true damage against targets below 25% health.
(i.e. level 18 Smite deals 1150 true damage instead of 1000 true damage, this is to help with securing objectives like Baron Nashor or Dragons with that tiny bit of extra damage.)
I would rather see Smite go back to being all about PvE combat for the most part, though this adds vision control elements for some of the ideas, rather than granting a combat advantage against other champions. This should tone back jungler power and bring them back to a better state because the supportive roles probably should be supportive roles, not everyone needs to be a carry since that defeats the purpose of having a middle and bottom to funnel gold into so they can carry the game, junglers (and obviously supports) should be the supportive positions for their team that sets up their team to do well rather than solo carry on their own without their team.
For the record, Spectral Smite is a gimped Twin Shadow's ghost pretty much, weaker in every way including the fact that you only get one ghost at a time, granted Smite does come with two charges so the frequency between ghosts is up more often. Also a reminder that you can only get one upgraded smite at a time just like now.