I have two nominations, which may or may not be controversial:
Aromatisse to A:
My main argument here is Aromatisse's lack of self-sufficiency. Sure, its really bulky and has a nice typing, but for a wall, it is worn down very quickly. It has to heal itself literally after every single powerful attack in order to switch in again. And since Wish takes two turns to activate, its opens up the way for the tier's most dangerous setup sweepers, like Cobalion, Durant, CM Reuniclus/Cresselia, etc. You can argue that Alomomola, or any wall has this problem, but Aromatisse's exacerbates this problem as its only option to heal itself is Wish, which again, takes two turns. If it decides to switch out, it basically can't switch in again on decently powerful attackers.
To illustrate my point, lets say you switch Aromatisse on a Hitmonlee's HJK after SR, taking roughly half your health. You can either choose to A) Wish/Protect, giving your opponent time to set up with his Durant (arbitrary sweeper) if he decides to switch out, B) Attack, killing lee if it decides to stay in, or C) predict a switch and switch out yourself. A) gives away a free turn, which can be disastrous, depending on your situation, B) either leaves you crippled at miniscule health or has the same effect as A, while C) leaves you unable to switch into that attack again, or any other moderately powerful attack. It's KOed by Crunch + Waterfall by Sharpedo, for example. Now you might say that any good player will carry another counter to Lee, or that Aromatisse is meant to check, not counter Lee, but replace Hitmonlee in the example with any other powerful attacker, and it becomes apparent the flaws of lacking a secondary healing method.
A lot of things that Aromatisse is commonly found with (Rhyperior, Doublade, and Weezing) that can cover Aromatisse's weaknesses to the multitude of hard hitting Steel-types are also reliant on its wish passing, meaning that usually only one pokemon is going to be consistently healthy. Aromatisse is rather self-defeating at all of its roles from a wish passer, to a cleric, to a wall, because it hates switching into attacks. Often, the only time you can succesfully bring it in to do its job is during a free switch-in. Aromatherapy makes this problem ten times worse, as it rarely can find an opportunity to use it. It also absolutely hates hazards, as that cuts its lifespan even more. Ironically, Aromatisse performs its best against against opposing stall teams, not offensive teams.
Notice that I'm nominating for A rank, and not any lower, because Aromatisse is still a good mon, its just that it can't really deal with the pressure of an offensive team very well.
Audino to B-/B:
Relating to my previous point, Audino is one of the best wish passers, with the combination of Wish + Regenerator. If you need a bulky water slot to counter Moltres, then Audino is something you should strongly consider as a wish passer. Unlike Aromatisse, it can actually switch out easily without always healing itself, and actually has better overall bulk, meaning it can stop many of the same threats that Aromatisse would stop. What makes Audino unique is its access to Encore, giving the niche of the only wish passer (or any wall, for that matter) not suspectible to setup sweepers, which is a huge boon for defensive teams. Sure, it can be played around, but at least its not a sitting duck in the face of things like SubBU Braviary, CM Psychics, and so forth. Also, it has access to Knock Off, Healing Wish, Thunder Wave, and Heal Bell, giving it nice options all around. It's weaknesses are obvious, including its weakness to Fighting (Lee, Virizion, Cobalion) and Taunt, but its definitely better than most of the C+ rank.