While Throh is easily an S Rank Pokemon thanks to its awesome coverage (Fighting and Dark cover everything but Fairy, and all Fairies in the tier outside of Carbink cannot afford to lose their items whether it's an Eviolite or a Choice Scarf), its great bulk, and the fact that most Pokemon have a hard time switching into it successfully, I still think even despite all of this that Throh does not deserve a ban.
Throh is a Pokemon that I've had extensive experience using since the post-Musharna meta, and so I'm well aware of Throh's limitations. Throh can beat either Stall with its Taunt / Toxic set or Offense with its RestTalk set, but it obviously can't run both sets at the same time. If you attempt to run Taunt / Toxic to beat Stall and you happen to encounter Offense on the ladder, Throh is worn down too quickly, especially given the fact that it has so many checks in the tier.
For example, Jumpluff, Kadabra, Leafeon, Torterra, Nastypass Togetic, Mr. Mime, LO Swanna, CB Dodrio, CB Zweilous, Offensive Pivot Pelipper, SF LO Zen Headbutt Rampardos, 44 Spe Specs Beheeyem (provided Throh isn't running more speed), CB Luxray with Intimidate, Coil Arbok with Intimidate, Guts Adamant Ursaring (and many more) can all OHKO or 2HKO Throh without being OHKO'd themselves, even if most of these can't switch in directly.
I did not list every check that exists in PU, but the point is, there are many; enough to the point that Throh struggles after it scores a KO because it is too slow to take on the revenge killer in most cases. If Throh were faster or carried priority to handle its revenge killers like Kecleon did, I'd argue for a ban for sure, but the fact is there are too many faster checks in PU to logically justify a ban.
Additionally, its standard moveset of Knock Off / Storm or Circle Throw / Rest / Sleep Talk plays fairly inconsistently because Sleep Talk only lets you damage your opponent 66% of the time. This, in conjunction with its many checks, means that there's a possibility your opponent's check to Throh will be able to switch in directly after a Rest and set up on you as you select Rest again (or simply Taunt you out of Sleep Talk) - Dundies' Leafeon up above was a good example.
Finally, I don't think banning one of two fully evolved Fighting type Pokemon will be healthy for the PU metagame in the long run. This by itself would be clearly limiting to PU because if you wanted a solid answer to Knock Off in order to keep your team's items in tact, you'd be forced to run Carbink or Poliwrath pretty much. Consequently, if you were forced to run either Poliwrath or Carbink for Knock Off absorption (Carbink isn't even a safe option because Pawniard exists), your team composition would be too limited to run an offensive Water type, like SS Huntail, SS Carracosta, SS Barbaracle, Floatzel, Kingler or Basculin, as there would be too many type weaknesses in common (e.g. Water + Water, Water + Water/Rock, Rock + Water, or Rock + Water/Rock).
There are a few more reasons why Throh shouldn't be banned, but I'll leave it there for now! I may also post on Sneasel later, but it seems like a clear ban to me at this point.