I really want to love this champion but it feels like she has no agency compared to other supports. I switched to a Nami game after playing Yuumi all week and immediately felt like I was playing a totally different game, one where I mattered. I don't think Yuumi is ever going to get above 45% without some changes- and i dont think "buffs" is really the right word for what she needs, I think she legit needs changes to her ultimate in order to have agency as a champion. Yuumi only has 1 damage skill so her Ult needs needs NEEDS to be impactful and right now it's just... well, the enemy flashes it or they just stand in it and kill you through it. The cooldown is so long that it isn't up every fight and if it's down then she's so... useless...
Like I play Neeko support and Neeko's ult is incredibly better than Yuumi's and has like half the cooldown. Neeko has to play well to get into range to use it sure but aiming Yuumi's ult is actually harder because you have to deal with moving through the fight and healing people during it because it's not a stun and the enemy is still actively murdering your team while you're ulting.
Her lane phase is probably fine but her ult needs help. Either make it a stun or extend the length of the root if you continuously land waves or just bump the damage numbers on it so that her teamfight damage isn't so poor. It's SO HARD to cast q's in a teamfight because you're almost always too close and it just pops on spawn and does crap for damage and NO slow. Yuumi should shine in teamfights but right now she only does if your team is already ahead. You don't win the game because of a clutch Yuumi anything. And that's... depressing as a support main. My skill is irrelevant if my solo lanes/jng aren't winning, and Yuumi is extremely poor at securing lane kills so you win the lane on attrition/farm but get few if any kills to bolster the team...
I'm trying to like her. I'm trying so hard. I don't play as a backpack, I use my passive constantly, I even get first bloods fairly often nowadays, but Yuumi's lane is so vulnerable to ganks it's disgusting so you just get 3-4 man dove all the time and it's so miserable I can't even justify picking it anymore. And then coming to the boards and reading "Dont buff my secret OP 40% win rate champion" is like, are you effing kidding me????!