I think yuumi should have a detached w cd

Of 4/3/2/1/0 seconds (starting from the moment she detaches), scaling with W level. A good yuumi can currently be attached for the whole W cd, bounce towards an enemy, auto for shield, and reattach to her adc before most enemy attacks can land, then immediately q. It makes her more uninteractive in lane than I believe she deserves to be, and by making her choose between leveling that for safety and other abilities for stats I think you get a proper tradeoff.