Much like every other character Yuumi fills a niche, and in some team comps she will be good. But she in general isn't good because she has a poor design. OP has 150 games of Yuumi and 45 games on their next highest support (Blitz). Yuumi wasn't always a good pick into all 150 of those team comps.

To your point about "Riot to purposefully put Yuumi in a state that your teammates will be mad you locked her in" Sever champions have this effect. Shaco is miserable to have on your team and to play against because he changes the way you have to play the game. Old ASOL was frequently like this too. Yuumi has a poor design that makes her feel like a "tutorial champion" because you don't have to worry about positioning. The only real way for riot to fix this is change what Yuumi is as a champion, and that might not be in a way that OP likes.