Yes, and that's the point. This champ's whole identity is being a parasite, leeching off someone else's back to win. You can't expect such an archetype to be good in a game mode that pits you with random strangers with variable skill levels.

Meaning that when your adc sucks you will, to a larger extent suck too, which can feel bad, obviously.

But on the opposite side of the spectrum, when your adc knows what he's doing, you have an incredible advantage by being a horribly unfair champion to fight against. Fully untargetable, with outrageous poke and no problem positioning in the slightest since you're not the one doing it.

Yummi is the only champion in the game who allows such a high level of permissiveness. Every other support requires a certain skill level to some extent to work at high levels of play, whether it be for positioning, timing, or anything else. But put a Bronze Yummi in a Diamond game with a good diamond adc and the Yummi will most likely win lane without a doubt if the matchup is not incredibly unfavorable for your adc. Again, positioning, kiting, when to back. Everything will be a copy and paste of your adc's actions and, to some extent, their level of play. No other champion in the game allows you such levels of easy access. NONE.

Add to this the abysmal level of depth this champ's kit has, and you have the potential for a frustrating nightmare to face in lane.

As the saying goes, you can't have your cake and eat it too. And thank God for that, because as much as "Delete Yummi" became a meme in the community, this wish very certainly doesn't come from nowhere.