After only a single Rapid Spin it has the potential to become unstoppable due to its natural bulk that allows it to survive even SE special attacks in tandem with its monstrous attack stat that often means setup isn't even required (unless you count Rapid Spin as setup).
252 SpA Iron Crown Psychic Noise vs. 0 HP / 0 SpD Great Tusk: 390-462 (105.1 - 124.5%) -- guaranteed OHKO
0 SpA Iron Valiant Moonblast vs. 0 HP / 0 SpD Great Tusk: 398-470 (107.2 - 126.6%) -- guaranteed OHKO (assume this is mixed)
252 SpA Kyurem Freeze-Dry vs. 0 HP / 0 SpD Great Tusk: 380-450 (102.4 - 121.2%) -- guaranteed OHKO
0 SpA Liquid Voice Primarina Psychic Noise vs. 0 HP / 0 SpD Great Tusk: 326-386 (87.8 - 104%) -- 25% chance to OHKO
0 SpA Zapdos Hurricane vs. 0 HP / 0 SpD Great Tusk: 476-564 (128.3 - 152%) -- guaranteed OHKO
132 SpA Iron Moth Energy Ball vs. 0 HP / 0 SpD Great Tusk: 316-374 (85.1 - 100.8%) -- 6.3% chance to OHKO
If its max hp, it maybe can survive the hit, but I wouldn't say this is necessarily amazing hittaking. In a realistic game, tusk isn't going to always be max hp, so even non stab super effective hits will be KO'ing it.
It has the coverage options to easily beat ALL spinblockers (yes even FRAUDcha) and is a pain in the ass to stop from spinning as after spinblocking you basically have only a single turn before the enemy clicks a much stronger attack.
And? What does this have to do with anything? Most of our spinblockers lose to our rapid spin users. Treads can defeat all besides maybe sinistcha (but even then it doesn't like taking ice spinner), excadrill also blows them up besides maybe sinistcha and quaquaval annihilates them with aqua step or knock off (besides sinistcha again, but like, cool).
In order to reliably beat it you need a robust physical wall, usually a Rooster, or something that outspeeds even after a boost and can hit it SE, or SE priority (which is really only Aqua Jet because nobody uses Weavile anymore), OR you just hit it hard, accept that a mon will die, and THEN nuke it with priority, and of course, you can also just have the right Tera.
And all of these are fine? Like, most of our physical walls do decent against tusk, the metal birds are great, sinistcha can still beat it with strength sap, gliscor can take one hit from it and toxic it in return, zamazenta can id up with it or roar it out, zapdos and moltres screw it over with status/big damage, alolomola just doesn't care about it at all lol, landorus can take one hit and intim it and dondozo is there if you really need it. Most teams will either have a choice scarfer or booster energy mon, and guess what? Most of them hit it super effectively. Valiant moonblasts it into oblivion, iron moth fiery dance does ton to it or energy ball just OHKO's it, scarf darkrai hits it with ice beam, deoxys speed psycho boosts it, scarf enam moonblasts it, scarf meow hits it with flower trick (which does 50% to it, but it can always survive an ice spinner from full).
Also rillaboom exists, which while it is on the downtrend, is still great at hitting tusk for big damage. Also people still use weavile, its a good mon in the tier and handwaving away isn't doing anything.
None of that is particularly hard to do or to fit on a team, but if you don't have at least one of those things at the ready when the elephant is about to spin or has already spun, it's basically guaranteed that Tusk is going to flatten what remains of your team.
This happens for most mons (when teambuilding, your team should already have 2 answers AT least for tusk, you get those answers by just making a good team, speed control is really important for teams and unless you are making HO, your team will have a defensive wall), when you remove there answers, a mon goes crazy. Remove primarina's answers, and it will probably win. Remove okidoki's answers, and it will go crazy.
I don't think it should be banned, but I do think that people need to stop hailing it as some paragon of a healthy metagame.
It is a paragon of a healthy metagame, and saying otherwise is silly. It provides a defensive backbone to teams while not being dead weight offensively (but not being overbaring offensively too). It also is very important because it is probably THE BEST hazard remover in the game, bar none. It CAN sweep, but that's fine, it has to get multiple boosts to OHKO things (which is important cause headlong rush reduces its defense stats, e-quake is only good on defensive variants), and still has mons that naturally wall it.