I know many will disagree with me here, but listen, the reason why I'm making this article is because of how overpowered Chien-Pao is in the Almost Any Ability metagame, since it's extremely fast, has tons of coverage moves such as Sucker Punch and Ice Shard, can constantly OHKO any other Pokémon on the battlefield beffore they last, and the only counter that it has is Toxapex but even then Chien-Pao learns Psychic Fangs when Toxapex is weak to Psychic Fangs since Poison is very weak to Psychic and due to the sky high Attack of Chien-Pao, it can KO Pex in an unlikely situation with either having the move be boosted by Strong Jaw or Tough Claws, and it's Dark/Ice typing allows it to hit any Pokémon such as Dragonite and Gengar for super-effective damage since even if Dragonite uses Aerilate boosted Extreme Speed, Chien-Pao can hold a Focus Sash and OHKO it with an Ice Shard or an Ice Spinner, as a solution to prevent it from getting OHKO'd.
It also can heal itself with Recover and has an ok 90 base SP Attack stat where it can hold Choice Specs and use moves like Dark Pulse and Blizzard to destroy any of the Pokémon that are weak to it with Sheer Force, just like Noivern did with Boomburst in Aerilate.
Again, disagree with me or not, but we need to stop being unfair to Weavile and ban it's new superior counterpart, Chien-Pao because he's way too fast and strong to have in this metagame and since Weavile got nerfed, that means there's another reason to Ban Chien-Pao since it counters so many of the Pokémon in the metagame that it's absolutely considered ban-worthy, now I'm not doing this to upset anyone or attack the administers or anything like that, I'm trying to say that this certain Pokémon has been nearly dominating the entire AAA metagame for a while now and it needs to be suspected about seeing it's either ban-worthy or not since it's used by many to abuse it's raw power and strength and since it's a Legendary, that's leads to more suspicion for a voting poll to see if it needs to be banned or not.
Sorry for that massive rant, I may have been a bit too harsh here but all of this is something I've witnessed since I have been playing Pokémon Showdown since Gen 9 was released and I've noticed that a lot of players in the AAA metagame use a Chien-Pao on their teams, and abuse it's power, so this needs to be considered and suspected.
I could see Chien-Pao eventually being problematic enough to get banned (after all, Weavile got banned last gen), but just wanted to point out some counterplay that you're perhaps missing:
DEFENSIVE:

Corviknight @ Leftovers
Ability:
Intimidate
Tera Type: Flying
EVs: 252 HP / 252 Def / 4 SpD
Bold Nature
- Body Press
- U-turn
- Roost
Corviknight switches in and can put loads of pressure on basically any realistic Chien-Pao, limiting them to having to go for Icicle Crash flinches to actually win the matchup. Body Press autowins the one-on-one, but you can also U-turn into some other things on this list (Triage Hatterene, a [faster] priority user, etc.). Even without intimidate, Corviknight actually eats attacks from Chien-Pao decently well.

Dondozo @ Leftovers
Ability:
Magic Guard / Intimidate / Tablets of Ruin
Tera Type: Water
EVs: 252 HP / 252 Def / 4 SpD
Impish Nature
- Curse
- Wave Crash
- Rest
- Earthquake
Pretty self-explanatory switch-in. Dondozo is simply too fat for Chien-Pao in most cases and can afford to just set up or just 2HKO even with +0 Wave Crash.

Quaquaval @ Heavy-Duty Boots / Covert Cloak
Ability:
Intimidate
Tera Type: Water
EVs: 248 HP / 252 Def / 8 SpD
Impish Nature
- Low Kick
- Roost
Admittedly not as popular as the Magic Guard (which can also check Chien-Pao) set and definitely still struggles against Psychic Fangs (which isn't a common set anyway), defensive Water/Fighting type is an obvious check to the Dark/Ice type, so I doubt this needs any explanation.

Scream Tail @ Leftovers
Ability:
Unaware
Tera Type: Fairy
EVs: 252 HP / 252 Def / 4 SpD
Bold Nature
IVs: 0 Atk
- Wish
- Protect
- Calm Mind
- Dazzling Gleam
Yeah...Chien-Pao is never getting past this without the hax of a lifetime. Crazy good mon btw.
OFFENSIVE:

Hatterene (F) @ Life Orb
Ability:
Triage
Tera Type: Psychic
EVs: 252 HP / 4 Def / 252 SpA
Modest Nature
IVs: 0 Atk
- Draining Kiss
- Mystical Fire
Triage-boosted Draining Kiss OHKOes or 2HKOes sash variants, and you can even just go for Mystical Fire if you fear a Queenly Majesty set or something (Chien-Pao can't OHKO Hatterene with any move unless it's Choice Band + Adamant + Sword of Ruin, which will announce itself pretty quickly anyway).
Slither Wing @ Choice Band
Ability: Tinted Lens
Tera Type: Bug
EVs: 252 Atk / 4 SpD / 252 Spe
Adamant Nature
- First Impression
- Close Combat
- Wild Charge
- Will-O-Wisp
Another priority moment, beats all the non-Queenly Majesty/sash variants.

Kingambit @ Leftovers
Ability: Doesn't really matter
Tera Type: Dark
EVs: 104 HP / 252 Atk / 152 Spe
Adamant Nature
- Swords Dance
- Kowtow Cleave
- Iron Head
- Sucker Punch
Usually wins if they aren't Sacred Sword.
And you already mentioned Dragonite so I won't go into that, but just wanted to lay out some more good examples than the ones given.
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I think with how common physically defensive Corviknight (particularly setup and body press variants) is right now, it's hard to make a good case for a Chien-Pao ban--after all, there's a Pokemon that beats it and also happens to fit on every team you can conceivably build LOL. The surprise factor of trying to revenge kill a priority-immune or sashed Chien-Pao and losing your Pokemon can be really annoying, but realistically those sets are somewhat telegraphed and are weak enough (due to lack of boosting ability/item) to still play around regardless. Hope this helps :P