I feel like Yuumi design of being totally untargetable and still being able to make full use, hell even use it more effectively, and she seems to have very few punishes, especially at high levels of play where mistakes like getting caught out happen less and less. It's not like the W has a long windup or a slow travel time, hell it outruns Rakan W by a mile in both of those criteria.
So how do you make the rest of her kit useful, without making her totally broken or totally useless. Because if she's at the power level of other supports, she's going to the definitive support, as she's nearly impossible to kill, so you're getting all the rewards of a support with very little consequence. However, if she's put at a power level that compensates for her long winded life, wouldn't you pick another champion that has actual numbers? To me, there doesn't seem to be a good sweet zone, it reminds a lot of Kalista where her kit is so greatly powerful she can't be kept at the same numbers of other champions.