Sound logic. But how about instead of playing a poor champion in a traditional style which runs counter to how they're designed. Play a real support who's designed to just work? Everytime someone mentions Yuumi not being good, there's the pullback of "She's New." "People are playing her wrong." But the reality is, she's just not good. It's cool your logic is 'try not afk attaching to her and see how that goes' but have you ever stopped to think that maybe you'd pick another support for that? Most Yuumi I've seen try detach and reattach mid-fight as you suggested which is fine for the Yuumi, and awful for the ADC. It's a nice gimmick, and sure with some number buffs could be good.
But saying people are playing her wrong just because it doesn't work isn't fair. At this point, they're using her abilities as expected and it works as expected. It just isn't very good. Also everyone saying 'people are jumping to conclusions too early', I haven't seen one person come out and say "She's not total garbage." Just alot of people saying "It's unfair to say she's total garbage." Those two things don't mean the same thing.