
While this mon does have counteeplay, mostly in Aegislash, teams without a Ghost type are bound to get steamrolled by this mon after hitting with a Close Combat, amd triggering White Herb. And even if it wasnt an issue now, it will become an issue IF the Terrains and their corresponding seeds where to return to the scene, in which case, it would simply be unbearable.

One move, Shell Smash

This mon screams nothing but trouble
Agreed on all 3 points. I've used all 3 mons, and while the other 2 are absurd too, the standout ban for me is

Sneasler.
Sneasler is what I call a "Just use priority" mon, where it has insane speed and power and priority is the only counterplay for offensive teams. The problem is the tier is full of these mons (Blatoise, Zam, Gengar, Delphox, Espathra, and also dozens of niche mons after a boost), so many or even all of your prio mons/defensive pieces might be dead by the time Sneasler comes in.
Not to mention everybody is taking rocks damage, and clearing hazards can be difficult when a turn using rapid spin or defog might be GG as a blastoise clicks shell smash and kills you
and then the real problem of Sneasler that sets it apart from the rest.
This thing has ridiculous set variety (I've seen each of White Herb, Sitrus, Sash, and Poison Touch several times so far), when you see it you never know what it might be. If you guess that it has the wrong set, you can sometimes just lose the game on the spot. And even if you guess right you usually still lose a mon because of how powerful this thing is, which can mean a lost game if another broken mon is able to capitalize
- White Herb is by far the most reliable to activate, but it takes more time to get going cuz it has to click CC and SD separately... unless you're running a webs team, then you lost the game on the spot, thanks for playing. If you can't kill this thing fast enough it can just win
- A bulkier Sitrus set can click SD and survive with 50-70% HP after Sitrus, which is enough to live weaker priority attacks that would have been able to handle the other sets (or weak hits from defensive mons). If you only had 1 prio user left, it's game over
- Sash is imo weaker because any hazards or priority kill it, but it can still cheese out wins in the lategame by outplaying sucker punches or if your priority users are dead (a common case in this metagame). And as a bonus it can revenge kill any sweeper if hazards are kept off
- Sash Reversal is also super funny if you can manage to proc it, you can do things like 2HKO pex on the switch and OHKO corviknight
- And lastly Poison Touch can sometimes work, because Sneasler's natural speed tier is already high even without Unburden. So if you're not expecting the extra 20% or so + possible poison from Fake Out, your counter to sneasler can suddenly crumble to dust (especially if your revengekillers or walls are chipped from countering all the other brokens in the tier, prio mon comes in at 45%, takes 12% from rocks, 25% from fake out, 12% from poison, and bam you lost the game gg)
- haven't tried it but poison touch with fake out + uturn might be able to wear down some of its defensive answers too, although at least things like Aegislash or Pex are poison immune
that's not even all, I bet someone out there is running Fling or Lum Berry or a resist berry (all of which are real sets IMO), and if Sneasler is in the right situation for that item, it just wins
Same for defensive counterplay (as little as there is) being thwarted by random moveset adaptations. A Throat Chop Sneasler can kill the Aegislash you thought would be able to handle it (Shadow Claw crit or Fire Punch could do something too although they don't reliably kill). Gunk Shot over Dire Claw can pick up an unexpected kill. Quick Attack can beat a Palafin or a Kingambit trying to revenge it
And there might be more, I tried out Sash + Counter and was able to kill a +4 def corv as it used brave bird
and once Sneasler gets an inch, it takes a mile and can easily pack you up. Insane amount of power for a mon that doesn't take a mega slot, can't be copied by Ditto, and can easily adapt to item clause
OH and I totally forgot that Dire Claw can just randomly put the target to sleep, and instantly win the game, cuz it's turbo rare for there to be multiple mons on a team that live 2 hits from boosted sneasler