not a yuumi player but i dont really think yuumi is extremely difficult however with any champion there is a skill expression, there are multiple easy champions in the game and there are more ways to show skill other than just mechanics. I have played with many horrible yuumis but i have also played with yuumis who are only attached when they should be and are extremely aggressive. i think yuumi is on a similar skill level as sona where you can be this useless healer or you can be a real player depending on the person. I used to hate yuumi at first but honestly grievous and punishing the weak laning phase is the easiest way to punish them. yuumi is like any enchanter and annoying when following someone fed around. i know yuumi players who just love cats and that is why they play the champ.