I'd really like for Aipom to be raised.
It hits 19 speed, can 2HKO the vast majority of the metagame, and is insanely versatile. Other than the few very fast taunters and scarf multihit users, Aipom is the only relevant pokemon that can reliably prevent Surskit from setting up Sticky Web. Aipom also possesses a very fast taunt along with other support options like Thunder Wave or U-turn. Aipoms movepool is chalk-full with helpful options. Fake Out and Fury Swipes are, for the most part, necessary, but it has a lot of flexibility outside of that. Between Knock Off, Brick Break, Fire Punch, Ice Punch, Seed Bomb, and Gunk Shot, near nothing can switch in. Aipom's bulk is often understated as well, but for reference it's bulkier than Mienfoo. Furthermore, Aipom will rarely have a bad team matchup because its strong Fake Out and Speed allow it to beat offensive mons, while Little Cup rolls with Fury Swipes, coverage options, and bulk let it easily beat common bulky pokemon.
Now obviously there are downsides to using Aipom and I'll talk about them so that I'm not appearing to be completely biased here. Aipom has no resistances, so switching in is very difficult. Using Aipom can be very prediction reliant. Fury Swipes also has some downsides such as forcing you to almost kill yourself on Ferroseeds and essentially guarantees that Larvesta or Ponyta will burn you. 80% accuracy can be annoying. If you're not using a Life Orb, you have to use Knock Off on near everything before you get good damage rolls. Even with a Life Orb, an adamant nature is needed to get good rolls against particularly bulky pokemon like Spritzee. Aipom frequently causes 50/50s that can result in you killing your momentum. All forms of status also greatly hinder Aipom.
To sum up, Aipom does have flaws but it can bring many valuable assets to a team, while needing little team support, fitting the B-rank definition. Aipom does not have a big flaw preventing it from being effective, does not require significant support, and does not face competition with more commonly used Pokemon, so being in C-rank just doesn't make sense.