Jungle Yuumi is possibly extremely overpowered at the moment. There are a number of changes making this better and ill go into each one. The changes are based on
1) Every change to Yuumi pushing her into more aggressive potential rather than passive potential
2) Early rift heralds being more potent
3) Mana on bop + Glacial augment buffs.
So, to start things off, top lane is a much easier match for the Yuumi pair than bot, lacking range harass AND jungle presence makes laning as a melee far easier, and the lane is at max a 2v2 instead of a 3v2. Yes, this leaves bot open for free jungle presence, but if left uncontrolled the top lane will completely steamroll in map presence.
Zoomies changes all point toward aggressive play. Top has a lot more easy of a time having aggressive play than bot does for the stated reasons. A bigger heal means you don't have to wait to use it and can top off with it, and a non decaying slow makes roaming and chasing easier.
Attack speed makes brawling better, but the more important reason is for taking turrets, jungle camps, and rift. The ability to take jungle camps means you can clear your buff and sometimes the enemy buff FOR FREE. Yuumi can tank both buffs and set both of you ahead and the enemy jungler behind. These are all EXCLUSIVE to top lane jungle, you cannot do any of these effectively as bot/support.
Glacial augment buffs combined with bop buffs give you even higher bully power against lone champions and melee champions. Combine this with Twin Ghosts you effectively secure a kill almost any time. Hopping out for a bigger shield, mana, and a slow means that the opposing top laner basically cant do anything. It either sets the pair up for an engage, or allows Yuumi to get free poke. There is no inbetween.
Early rift changes are easy gold, Higher early damage means more plates, and multiple rifts means the pressure top is far more substantial than bottom/support. Higher pressure and yuumi tanking it makes clearing it SUPER EASY. Once again, Zoomies makes clearing rift, scuttler, and buffs far easier.
The best part of Yuumi top is OPTIONS. You can choose standard spellthiefs edge for excellent laning or blue smite for extreme roaming pressure.
On top of all this, the enemy jungler is put into a predicament. They can either
A) Camp bot, and get near free dragons, but top and mid will steamroll. A botlane conscious of whats happening can play safe and mitigate most jungler influence.
B) They can camp top, but the pair still wins most trades as the enemy laner is behind and the pair has been capitalizing. This frees other lanes from jungler influence, and STILL puts the pair ahead.
C) They can spend their time clearing Yuumi's uncleared camps. This essentially frees every lane from jungle presence by them having to juggle two jungles worth of camps.
The dragon changes make early dragons less potent, so the cost of losing 1 or 2 is less than it was last season. The dragon only starts to really matter 3rd and 4th kill, in which case the top laner has already started roaming with his lead.
Yuumi jungle works best with roaming or hard diving tops. Darius, Volibear, Pantheon, Fiora, Camille, the standard. However, it does have its bad matchups. Depending on your pair, enemy champions top can be problematic (Namely Jax and Kayle). If your mid roams, its better for you. Do NOT play hard farming champs like Nasus, Yorick, and Tryndamere.
TL;DR This last patch put a serious amount of power into the Yuumi Jungle/Top pair that cannot be harnessed or used effectively in a bottom/support pair. With good enough play it is near impossible for the enemy team to react and recover. Rift changes, Yuumi changes, and Glacial Augment was a very clear oversight into this result.