Great Tusk may actually be the coolest #1 usage mon ever for this reason: it's never seen before for the #1 usage Pokemon to be good at just 1-2 things. Landorus-Therian has many roles whether it be scarfer, spdef tank, defense invested pivot etc. Snorlax needs no mention, Latias and Jirachi in DPP have heavy versatility as well. Great Tusk and Kingambit as well kind of do just 1 thing, with Great Tusk of course to a lesser extent. In regards to Tusk its a defensive wall that has good immediate damage and semi-setup capabilities with Rapid Spin. It doesn't have roles outside of that, sure there's speed control with booster energy but it's still kind of the same thing a bulky attacker that has some setup capabilities. It's has some of the least versatility in role potential and set potential out of any #1 usage Pokemon, besides Kingambit who also has a similar thing going. Kingambit is a bulky attacker who turns into a late game cleaner, there's nothing else it really does.
BUT I think the coolest aspect of this is because Great Tusk/Kingambit lack versatility in options, when the meta changes to hurt Kingambit or Great Tusk, it's up to these Pokemon's allies to limit the negative meta changes. This is a bit of a complex idea but for example when Moltres became more popular this obviously hindered Great Tusk due to Flame Body. Unless you run troll Head Smash, you'll have to change your TEAM STRUCTURE to accommodate for new weaknesses Great Tusk has as it's a limited Pokemon. We saw these changes as well, Great Tusk + Garganacl bulky offense has become a more popular idea as Tusk Knock's molt and from there Garg forces pressure with Stealth Rocks or Salt Cure since it comes into Moltres everytime which will happen if you are using Great Tusk. For the first time ever the BEST Pokemon, can't adapt (outside of Tera ESPECIALLY in regards to Kingambit) which makes for some really interesting changes to team structures as the metagame changes over time.
In regards to the opposite where a good Pokemon is constantly able to adapt to meta changes, look no further than SS OU. Landorus-Therian was running defense invested sets for a while until it received more pressure from Pokemon like Dragapult, in which it changed to more Sp.Def orientated EV spreads.
Example of current BO garg + tusk team in high ladder:
https://replay.pokemonshowdown.com/gen9ou-2210513777