Yuumi doesnt have a learning curve
Go play dota and try to play meepo. Thats a fucking learning curve. The player base of lol is just so bad that they cant handle slightly higher skill cap champs. Oh and mobility doesnt count towards high skill like yasuo and riven and etc. A High Skill cap champ or hero requires you to do what most other do not in such a way that only the most knowledgeable and capable players can achieve and abuse. Meepo needs control groups to activate his clones and if one clone gets caught out and dies well just say goodbye to the rest because each clone is the original which means if one dies you die and the rest die, with Yuumi you just afk sit in your carries and make them into the final boss of Castle Crashers with a fucking twist. The boss gets all the health potions and now you are sitting there wonder if this is actually fun to play against or if it is even balanced. You have yuumi mains saying she is hard. Thats a joke. I can play yuumi and hyper inflate my lp too, but I dont because I know how much of a joke that champion is to the game. You have new gamer developers coming into the scene who dont know what this game should be about. If you can spam heals and shields with no consequences or any way to remove her from the W then she will be unbalance-able forever. Pros will make her pick or ban because lets be honest. Pro games don't last long. Early game decides everything now. yuumi provides free farming for the adc in the lanning and becomes a monster after one item and then attaches to the bruiser carry. They even had to nerf aatrox healing aspect because of how broken yuumi heal was for the game. If you have to change other champions kits just to balance another champions kit that just shows how much of a joke and cancer this cat is the game.
If you are taking out key aspects of the game to improve your skill like positioning and conservation of resources or the risk of death, then that certainly lowers skill cap. Riot even said Yuumi was meant for LOW skill players who are NEW to the game. Which makes no sense. She teach everything someone should not do. Be a useless braindead/glorified item that later makes anyone into a one trick god.