Yuumi's abilities can slow, buff, heal, shield... She has a mobile AOE ultimate that covers a very large area. But most importantly - her W glues her to the one she's supporting and makes her untargetable. Which, basically... makes Yuumi the easiest - most dumbed down champion in league of legends. You can go premade with your 5 year old sibling or your grandpa if they play Yuumi - and just tell them when to press Q, E and R... Even if they never played LoL before - if they follow your directions (just pressing one of those 3 buttons when you say so) - they should be able to handle rank games at your level - and do as good as any other support.
Even more than that.... if you're capable of multitasking - Yuumi's the most viable champion to be played as a duo "by same user (a user playing on 2 accounts/computers - at the same time)". Since you don't have control her movements (being glued to the other champs) - only 3 of her abilities (mainly 2 - cause the 3rd is her Ultimate).
Based on her abilities - i'd take it Yuumi was made intentionally like that. To be played in a duo by people who don't play league of legends - and be just as good as the ones they're premade with. More exactly... Yuumi was probbaly made for girlfriends (the ones who don't know how to play LoL - and not whiling to try it with any other champ). It's the only champ that can be easily played - while doing other stuff at the same time (browsing social media, taking selfies or whatever). Since you only need one hand and 2 fingers.
This would also explain why this champion is a Cat! 😸
