Clearly, the central argument of the pro-ban side is that Crawdaunt can KO any Pokemon in the tier with the appropriate set by hitting its counters with the correct move/setting up SD upon switchin.
This may be true, but it doesn't make Crawdaunt broken. The lack of true counters is not at all something that's unique to Crawdaunt. As Hikari showed, the same thing can be said of Salamence: between LO special attacking sets and physical sets, it can 2HKO the whole tier. This also applies to Hydreigon (no guaranteed switchins: it can carry Iron Tail and Superpower!) Mamoswine (only truly countered by Alomomola), and Infernape (can OHKO or 2HKO everything in the tier with the right move), among others. Even Hoopa can 2HKO the whole tier with only three moves, no variability in its set is needed.
These Pokemon don't have ~~~~~true counters~~~~~; however, clearly none of them are broken. Why? Because all of these Pokemon still have reliable checks. All of them pressure stall and passive builds in general, but that doesn't mean we should ban them.
If your team is prepared for the Swords Dance set, it wont be prepared for the Ice Beam/Sludge Wave coverage set and this will lead to a loss at preview.
If your stall team consists of Forretress and 5 things that die to Outrage, or Blissey and 5 things that die to Draco Meteor, you're going to lose to DD Fire Blast / mixed Salamence and LO Superpower Hydreigon respectively. That doesn't make Salamence and Hydreigon broken, it just means it's a bad team because you failed to adequately prepared for two of UU's top threats. If your stall team is Chesnaught and 5 mons that are OHKOd by Crawdaunt, same thing applies. That's what "preparation" means: you have to account for all of a Pokemon's sets when you try to check it. Crawdaunt only has one set with one variable moveslot, unlike stuff like Salamence or Infernape, which are significantly harder to prepare for. I cannot imagine a scenario where a team loses to Crawdaunt "at preview" unless the team is horribly unprepared.
Stall will not become "unviable", it basically only needs two things to account for Crawdaunt: a bulky Grass-type / fat Salamence, and a bulky Water-type. The latter is pretty much ubiquitous on stall teams anyway, fat Grass-types are something that's already used thanks to Mega Swampert / Feraligatr / Mega Sharpedo, defensive Salamence is an amazing Pokemon for stall since it hard counters every Fighting-type and Defogs on many Stealth Rock users. Hydreigon is also a thing we're starting to see on stall and semi-stall (there was a stall team with Hydreigon that was used quite frequently in UU Open) to counter things like Chandelure and Mega Houndoom reliably.
It's a perfect Pokemon that is too good in the UU metagame.
Crawdaunt is FAR from the perfect Pokemon. Its horrible bulk means that its resistances mean literally nothing (252 SpA Chandelure Shadow Ball vs. 0 HP / 0 SpD Crawdaunt: 114-135 (42.6 - 50.5%) -- 96.1% chance to 2HKO after Stealth Rock), severely limiting its ability to safely get on the field. It even fears directly switching into some of the defensive Pokemon it can threate - like Gligar's U-turn, Slowking's Scald, and Doublade's Sacred Sword. It's easily checked by any faster Water-resist (of which there are a LOT given that Crawdaunt's basically the slowest offensive Pokemon available besides like Machamp) and even Water-neutralities like Cobalion and Zapdos. Many other people have covered this but people are still saying "IT HAS PRIORITY IT CAN DESTROY OFFENSE" when this is simply not the case. Crawdaunt isn't even the best offensive Water-type in the tier, let alone best Pokemon.
Do people who think Crawdaunt is broken because it has no true counters think that it's broken in OU too? Seems like the same arguments apply - it can kill Mega Scizor/Skarm/Quag with CB Crabhammers, Ferrothorn with Superpower, Mega Venusaur with CB Crunch. It can 2HKO anything on the switch with the appropriate item and move!