I Hate Yuumi.
I'm not complaining about her being annoying to play against or anything, i hate her design and how she play's. Here's what i'v noticed with every Yuumi i play with and this is also the reason i hope no other champion is made similar to her.
First: She's completely useless in lane against pretty much every other support.
She completely rely's on me to do everything for her, i have to risk my positioning to let her hit her Q against lanes like Blitzcrank, Pyke or Thresh. That's not good because of point 2.
Second: She doesn't have the same 2v2 power as any other support.
Losing trades is pretty much a given with her as your support since she can only heal twice and has high cooldowns. She has 1 less ability than most other supports at level 3 and the enemy bot laner/sup don't have to waist any abilities on her since she's constantly attached to you. This add's to the final point.
Third: She's a "Win More" champion.
Her lane phase is pretty much non-existent, it doesn't really matter what ADC you play what matter's is that the enemy botlane is worse than you, if their worse than you are then Yuumi is great! Yuumi works best when your winning because if your already winning she makes it a lot harder to kill you and her ultimate is really good, she's good when she's able to piggy back off of someone who's fed but her lane phase is so terrible that in plenty of cases she puts her ADC at risk of being pretty much useless since Supports dictate botlane so much in the early game. She lacks any really good poke like other Enchanter supports, she lacks healing in comparison to them as well even with 2 E casts and she lacks CC like tank supports. She's a jack of all trades and master of none and that really makes it a pain to play with her in the botlane.
What accentuates this even more is if she's on the enemy team, if she's on the enemy team and she happens to be able to make it out of lane phase with a fed ADC next to her, goodluck because she's gonna make it near impossible to kill the guy. If she's able to hook on to a fed carry she's gonna make your life a living a hell. If not, well, it's a 4v5 and she just gave you free LP.
The champion feels bad to play with and against, she's a glorified minion when behind and she turns carries into unstoppable juggernauts when ahead, that's not fun.