After Mence, Azu will be the second 'mon to be banned not because it's too good on it's own but because of Jirachis presence.
You can easily beat Azu on it's own, Azu + Amoo is not that tricky to beat either and full Azu setup will only work against certain matchups, is prone to misstakes and hard to pull off. Unless you got Jirachi. Against Azu Amoo it's often enough to throw some Goggles on something being able to touch Azu (which is not exactly uncommon) or simply capitalize on them being so incredibly slow (+ Amoo being passive af) and not play like an idiot.
Thing with Jirachi compared to Amoo is, most good mons have a way to seriously hurt the latter with an attack that'd also hurt Azu, while Jirachi simply doesn't care about those. Kanga, Gardevoir, Lati@s, Sylveon to an extent, Cresselia, Amoonguss, Diancie, Ludicolo, Hoopa, Kyurem, Venusaur + all the mons you could slap Goggles on (Aegi, Rotom, Thundy etc), just to name the most important ones. Same goes for other redirectors btw.
Regarding Mence it's the exact same problem: Mence itself is good but definitely not broken. It interacts nicely with Kanga and Gardevoir, checks some of the very common threats rn (I'd imagine Mence balances the usage of Volcanion and Heatran) but isn't untouchable whatsoever, it can easily be checked defensively (Cresselia, Cune, Rotom, Thundy, Aegislash, Mawile) and offensively (TR, Diancie, fast Ice attacks, fairy Hyper Voice, Rain, Deoxys, Darkrai). Except when there's a Rachi next to it. Oh it also tanks a +6 Aqua Jet and deals heavy damage in return.
Azu is just a mediocre mon overall. Don't ban it, ban the real reason why it's so good. After that, unban Mence. It solves nearly every problem this meta has.